/* ============================================================
   GESP Level 1 C++ Practice - Design System v2
   Inspired by oj.ybccode.com — clean, modern, professional
   ============================================================ */

/* ---------- Variables ---------- */
:root {
  /* OJ-inspired colour palette */
  --brand-primary: #7358FF;
  --brand-primary-light: #9B84FF;
  --brand-primary-dark: #5A3FE0;
  --brand-accent: #FF9E23;
  --brand-accent-light: #FFB960;
  --brand-light: rgba(115, 88, 255, .08);
  --success: #11B329;
  --success-bg: #E8F9EA;
  --error: #E53935;
  --error-bg: #FFECEC;
  --warning: #FF9E23;
  --warning-bg: #FFF5E5;
  --purple: #7358FF;
  --purple-bg: #EDE9FF;
  --blue-link: #257DF9;
  --bg: #F1F8FE;
  --bg-secondary: #F5F7FA;
  --card: #FFFFFF;
  --text: #2E3038;
  --text-primary: #2E3038;
  --text-secondary: #7B8394;
  --border: #E4E9F0;
  --shadow-sm: 0 1px 4px rgba(0, 0, 0, .04);
  --shadow: 0 4px 16px rgba(0, 0, 0, .06);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, .08);
  --radius: 14px;
  --radius-sm: 8px;
  --radius-lg: 20px;
  --radius-pill: 9999px;
  /* Shared gradient */
  --gradient-brand: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  --gradient-brand-shadow: rgba(102, 126, 234, .3);
  --font: "PingFang SC", "Microsoft YaHei", "Noto Sans SC", system-ui, -apple-system, sans-serif;
  --font-code: "Cascadia Code", "Fira Code", "Consolas", "Courier New", monospace;
  --max-width: 1080px;
  --nav-height: 60px;
}

/* ---------- Reset ---------- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  font-family: var(--font);
  color: var(--text);
  background: var(--bg);
  line-height: 1.7;
  font-size: 15px;
  min-height: 100vh;
}
a { color: inherit; text-decoration: none; }
button { font-family: inherit; cursor: pointer; }
img { max-width: 100%; }
ul, ol { list-style: none; }

/* ---------- Layout ---------- */
.container { max-width: var(--max-width); margin: 0 auto; padding: 0 24px; }
.page-body { padding-top: calc(var(--nav-height) + 24px); padding-bottom: 48px; }

/* ---------- Navigation (Frosted Glass) ---------- */
.nav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  height: var(--nav-height);
  background: rgba(255, 255, 255, 0.65);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid rgba(228, 233, 240, 0.6);
  display: flex; align-items: center; padding: 0 28px;
}
.nav-brand {
  font-weight: 800; font-size: 1.1em; color: var(--brand-primary);
  display: flex; align-items: center; gap: 8px; margin-right: 32px;
  white-space: nowrap; letter-spacing: -0.3px;
}
.nav-brand .badge {
  background: var(--brand-accent); color: #fff;
  padding: 2px 10px; border-radius: var(--radius-pill);
  font-size: .65em; font-weight: 700;
}
.nav-links { display: flex; gap: 2px; overflow-x: auto; }
.nav-links a {
  color: var(--text-secondary); padding: 8px 18px;
  border-radius: var(--radius-sm); font-size: .9em; font-weight: 500;
  transition: all .2s; white-space: nowrap;
}
.nav-links a:hover { background: rgba(115, 88, 255, .06); color: var(--brand-primary); }
.nav-links a.active {
  background: rgba(115, 88, 255, .1); color: var(--brand-primary);
  font-weight: 700;
}
.nav-user {
  margin-left: auto; display: flex; align-items: center; gap: 8px;
  color: var(--text-secondary); font-size: .85em;
}
.nav-user .xp-badge {
  background: rgba(115, 88, 255, .08); color: var(--brand-primary);
  padding: 4px 12px; border-radius: var(--radius-pill);
  font-weight: 700; font-size: .8em;
}

/* ---------- Hero / Page Header ---------- */
.hero {
  background: linear-gradient(135deg, #EDE9FF 0%, #D6E8FF 50%, #E1F3FF 100%);
  border-radius: var(--radius-lg); padding: 40px 36px;
  margin-bottom: 28px; border: 1px solid rgba(115, 88, 255, .1);
}
.hero h1 {
  font-size: 1.65em; color: var(--brand-primary); margin-bottom: 6px;
  font-weight: 800; letter-spacing: -0.5px;
}
.hero .subtitle { color: var(--text-secondary); font-size: .95em; }
.hero .tags { display: flex; gap: 8px; margin-top: 14px; flex-wrap: wrap; }
.hero .tag {
  padding: 4px 16px; border-radius: var(--radius-pill); font-size: .78em; font-weight: 600;
}
.hero .tag-primary { background: var(--brand-primary); color: #fff; }
.hero .tag-accent { background: var(--brand-accent); color: #fff; }
.hero .tag-success { background: var(--success); color: #fff; }

/* ---------- Cards ---------- */
.card {
  background: var(--card); border-radius: var(--radius);
  padding: 24px; box-shadow: var(--shadow);
  border: 1px solid var(--border);
  transition: transform .2s, box-shadow .2s;
}
.card:hover { box-shadow: var(--shadow-lg); }
.card-clickable:hover { transform: translateY(-3px); cursor: pointer; }

/* ---------- Stats Grid ---------- */
.stats-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(145px, 1fr));
  gap: 14px; margin-bottom: 28px;
}
.stat-card {
  background: var(--card); border-radius: var(--radius);
  padding: 20px 16px; text-align: center;
  box-shadow: var(--shadow-sm); border: 1px solid var(--border);
  transition: transform .2s;
}
.stat-card:hover { transform: translateY(-2px); }
.stat-card .stat-icon { font-size: 1.5em; margin-bottom: 6px; }
.stat-card .stat-value {
  font-size: 1.9em; font-weight: 800; color: var(--brand-primary);
  line-height: 1.2;
}
.stat-card .stat-label {
  font-size: .78em; color: var(--text-secondary); margin-top: 4px;
}

/* ---------- Section Title ---------- */
.section-title {
  font-size: 1.05em; font-weight: 700; color: var(--text);
  margin-bottom: 16px; display: flex; align-items: center; gap: 10px;
}
.section-title::before {
  content: ''; width: 4px; height: 20px;
  background: var(--brand-primary); border-radius: 2px;
}

/* ---------- KP Grid ---------- */
.kp-grid {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr));
  gap: 14px; margin-bottom: 28px;
}
.kp-card {
  background: var(--card); border-radius: var(--radius); padding: 22px;
  border: 1.5px solid var(--border); box-shadow: var(--shadow-sm);
  display: flex; flex-direction: column; gap: 8px;
  transition: all .25s; position: relative; overflow: hidden;
  cursor: pointer;
}
.kp-card:hover { border-color: var(--brand-primary); box-shadow: var(--shadow); }
.kp-card-header {
  display: flex; align-items: center; justify-content: space-between;
}
.kp-card .kp-num {
  width: 34px; height: 34px; border-radius: 50%; display: flex;
  align-items: center; justify-content: center;
  font-weight: 800; font-size: .85em; color: #fff;
  background: var(--brand-primary);
}
.kp-card.completed .kp-num { background: var(--success); }
.kp-card-title { font-weight: 700; font-size: .95em; color: var(--text); }
.kp-progress-text { font-size: .85em; font-weight: 700; color: var(--brand-primary); }
.kp-card-stats { font-size: .78em; color: var(--text-secondary); }
.kp-progress-bar { height: 4px; background: #E4E9F0; border-radius: 2px; margin-top: auto; }
.kp-progress-fill { height: 100%; border-radius: 2px; background: var(--brand-primary); transition: width .4s; }
.kp-card.completed .kp-progress-fill { background: var(--success); }

/* ---------- Quick Actions ---------- */
.quick-actions {
  display: grid; grid-template-columns: repeat(3, 1fr);
  gap: 14px; margin-bottom: 28px;
}
.action-card {
  background: var(--card); border-radius: var(--radius); padding: 28px 16px;
  text-align: center; box-shadow: var(--shadow-sm);
  border: 1.5px solid var(--border); transition: all .25s; cursor: pointer;
  display: block;
}
.action-card:hover {
  border-color: var(--brand-primary); transform: translateY(-3px);
  box-shadow: var(--shadow);
}
.action-icon { font-size: 2.2em; margin-bottom: 10px; }
.action-title { font-weight: 700; font-size: .95em; margin-bottom: 4px; color: var(--text); }
.action-desc { font-size: .78em; color: var(--text-secondary); }

/* ---------- Wrong Answer Review ---------- */
.wrong-count {
  display: inline-flex; align-items: center; gap: 6px;
  background: var(--error-bg); color: var(--error);
  padding: 6px 16px; border-radius: var(--radius-pill); font-size: .85em; font-weight: 600;
}

/* ---------- Score Trend Chart ---------- */
.chart-container { padding: 16px 0; }
.chart-container svg { width: 100%; height: auto; }

/* ---------- Practice Page ---------- */
.practice-nav {
  display: flex; align-items: center; gap: 12px;
  margin-bottom: 20px; flex-wrap: wrap;
}
.practice-nav .back-btn {
  display: inline-flex; align-items: center; gap: 4px;
  color: var(--brand-primary); font-weight: 600; font-size: .9em;
  padding: 6px 14px; border-radius: var(--radius-sm);
  border: 1.5px solid var(--border); background: var(--card);
  transition: all .2s;
}
.practice-nav .back-btn:hover { background: var(--purple-bg); border-color: var(--brand-primary); }
.filter-tabs { display: flex; gap: 6px; margin-left: auto; }
.filter-tab {
  padding: 6px 16px; border-radius: var(--radius-pill); font-size: .82em;
  border: 1.5px solid var(--border); background: var(--card);
  color: var(--text-secondary); font-weight: 600; transition: all .2s;
}
.filter-tab:hover { border-color: var(--brand-primary); color: var(--brand-primary); }
.filter-tab.active {
  background: var(--brand-primary); color: #fff; border-color: var(--brand-primary);
}

/* ---------- Theory Section ---------- */
.theory-card {
  background: #F8F9FF; border-left: 4px solid var(--brand-primary);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 22px 28px; margin-bottom: 22px;
}
.theory-card h3 {
  color: var(--brand-primary); font-size: 1em; margin-bottom: 10px;
  display: flex; align-items: center; gap: 6px;
}
.theory-card h4 { color: var(--brand-primary-light); font-size: .9em; margin: 14px 0 6px; }
.theory-card ul { padding-left: 18px; }
.theory-card li { margin: 3px 0; font-size: .9em; }
.theory-card code {
  background: #1E1E2E; color: #CDD6F4; padding: 2px 7px;
  border-radius: var(--radius-sm); font-family: var(--font-code); font-size: .88em;
}

/* ---------- Question Card ---------- */
.question-card {
  background: var(--card); border-radius: var(--radius); padding: 28px;
  box-shadow: var(--shadow); border-top: 4px solid var(--brand-primary);
  margin-bottom: 20px;
}
.question-header {
  display: flex; align-items: center; gap: 10px;
  margin-bottom: 16px; flex-wrap: wrap;
}
.q-number {
  width: 32px; height: 32px; border-radius: 50%; display: flex;
  align-items: center; justify-content: center;
  background: var(--brand-primary); color: #fff;
  font-weight: 700; font-size: .85em; flex-shrink: 0;
}
.q-diff {
  font-size: .72em; padding: 3px 12px; border-radius: var(--radius-pill);
  color: #fff; font-weight: 600;
}
.q-diff.easy { background: var(--success); }
.q-diff.medium { background: var(--brand-accent); }
.q-diff.hard { background: var(--error); }
.q-type {
  font-size: .72em; padding: 3px 12px; border-radius: var(--radius-pill);
  background: var(--purple-bg); color: var(--brand-primary); font-weight: 600;
}
.q-body { line-height: 1.9; margin-bottom: 14px; }
.q-body pre {
  background: #1E1E2E; color: #CDD6F4; padding: 14px 18px;
  border-radius: var(--radius-sm); overflow-x: auto;
  font-family: var(--font-code); font-size: .88em; margin: 10px 0;
  border-left: 3px solid var(--brand-accent);
}

/* ---------- Options ---------- */
.options { margin: 12px 0; }
.option {
  display: flex; align-items: center; gap: 12px;
  padding: 13px 18px; margin: 6px 0;
  border: 1.5px solid var(--border); border-radius: var(--radius-sm);
  cursor: pointer; transition: all .2s; font-size: .92em;
}
.option:hover { border-color: var(--brand-primary); background: #F8F9FF; }
.option.selected { border-color: var(--brand-primary); background: #EDE9FF; }
.option.correct { border-color: var(--success); background: var(--success-bg); }
.option.incorrect { border-color: var(--error); background: var(--error-bg); }
.option.disabled { pointer-events: none; opacity: .85; }
.option input { display: none; }
.option-text { flex: 1; }

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 10px 24px; border: none; border-radius: var(--radius-sm);
  font-size: .9em; font-weight: 600; transition: all .2s;
  cursor: pointer; white-space: nowrap;
}
.btn:disabled { opacity: .5; cursor: not-allowed; pointer-events: none; }
.btn-primary { background: var(--brand-primary); color: #fff; }
.btn-primary:hover { background: var(--brand-primary-dark); }
.btn-secondary { background: var(--bg-secondary); color: var(--text); border: 1.5px solid var(--border); }
.btn-secondary:hover { border-color: var(--brand-primary); color: var(--brand-primary); background: var(--purple-bg); }
.btn-accent { background: var(--brand-accent); color: #fff; }
.btn-accent:hover { background: #E68A00; }
.btn-success { background: var(--success); color: #fff; }
.btn-success:hover { background: #0D9621; }
.btn-danger { background: var(--error); color: #fff; }
.btn-danger:hover { background: #C62828; }
.btn-outline {
  background: var(--card); border: 1.5px solid var(--border);
  color: var(--text-secondary);
}
.btn-outline:hover { border-color: var(--brand-primary); color: var(--brand-primary); }
.btn-sm { padding: 6px 14px; font-size: .82em; }
.btn-block { width: 100%; text-align: center; justify-content: center; }
.btn-group { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 16px; }

/* ---------- Feedback ---------- */
.feedback {
  margin-top: 14px; padding: 14px 20px; border-radius: var(--radius-sm);
  display: none; animation: slideIn .3s;
}
.feedback.show { display: block; }
.feedback.ok { background: var(--success-bg); border: 1px solid rgba(17, 179, 41, .2); }
.feedback.fail { background: var(--error-bg); border: 1px solid rgba(229, 57, 53, .2); }
.feedback .fb-icon { font-weight: 800; margin-right: 6px; }
.feedback.ok .fb-icon { color: var(--success); }
.feedback.fail .fb-icon { color: var(--error); }
.feedback .explanation {
  margin-top: 10px; padding-top: 10px; border-top: 1px dashed var(--border);
  color: var(--text-secondary); font-size: .88em;
}

/* ---------- Coding Solution ---------- */
.coding-solution {
  margin-top: 12px;
}
.coding-solution .code-block {
  background: #1E1E2E;
  color: #CDD6F4;
  padding: 16px;
  border-radius: var(--radius-sm);
  font-family: var(--font-code);
  font-size: 0.88em;
  line-height: 1.6;
  white-space: pre-wrap;
  word-break: break-word;
  overflow-x: auto;
  margin: 0 0 8px 0;
  border: 1px solid #313244;
}
.coding-solution .code-comment {
  color: #6C7086;
}
.coding-solution .code-block .code-comment {
  color: #6C7086;
}

/* ---------- Code Editor ---------- */
.editor-wrap { border-radius: var(--radius-sm); overflow: hidden; border: 1px solid #333; }
.editor-wrap .CodeMirror { height: 260px; font-size: 14px; }
.editor-toolbar { display: flex; gap: 8px; margin-bottom: 8px; flex-wrap: wrap; align-items: center; }
.io-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin-top: 10px; }
.io-grid label { font-size: .78em; color: var(--text-secondary); display: block; margin-bottom: 4px; }
.stdin-input {
  width: 100%; padding: 8px 12px; border: 1.5px solid var(--border);
  border-radius: var(--radius-sm); font-family: var(--font-code);
  font-size: .88em; resize: vertical; transition: border-color .2s;
}
.stdin-input:focus { border-color: var(--brand-primary); outline: none; }
.output-box {
  background: #1E1E2E; color: #CDD6F4; padding: 12px 16px;
  border-radius: var(--radius-sm); font-family: var(--font-code);
  font-size: .85em; min-height: 60px; white-space: pre-wrap;
  word-break: break-all; max-height: 160px; overflow-y: auto;
}
.output-box.err { color: var(--error); }
.output-box.running { color: var(--brand-accent-light); }

/* ---------- Test Case Table ---------- */
.tc-table { margin-top: 12px; display: none; }
.tc-table.show { display: block; }
.tc-table h4 { font-size: .85em; color: var(--brand-primary); margin-bottom: 8px; }
.tc-table table { width: 100%; border-collapse: collapse; font-size: .82em; background: var(--card); border-radius: var(--radius-sm); overflow: hidden; border: 1px solid var(--border); }
.tc-table th, .tc-table td {
  padding: 8px 14px; border-bottom: 1px solid var(--border); text-align: left;
}
.tc-table th { background: var(--bg-secondary); font-weight: 600; color: var(--text); }
.tc-table tr:last-child td { border-bottom: none; }
.tc-table tr:nth-child(even) { background: rgba(241, 248, 254, .5); }
.tc-table .pass { color: var(--success); font-weight: 700; }
.tc-table .fail { color: var(--error); font-weight: 700; }

/* ---------- Solution Panel ---------- */
.solution { margin-top: 12px; display: none; }
.solution.show { display: block; }
.solution pre {
  background: #1E1E2E; color: #CDD6F4; padding: 16px;
  border-radius: var(--radius-sm); overflow-x: auto;
  font-size: .85em; line-height: 1.6;
}

/* ---------- Pagination / Question Nav ---------- */
.q-nav {
  display: flex; align-items: center; justify-content: space-between;
  padding: 16px 0; margin-top: 12px;
}
.q-progress { flex: 1; margin: 0 16px; }
.q-progress-bar { height: 6px; background: #E4E9F0; border-radius: 3px; overflow: hidden; }
.q-progress-fill { height: 100%; background: var(--brand-primary); border-radius: 3px; transition: width .3s; }
.q-progress-text { font-size: .78em; color: var(--text-secondary); text-align: center; margin-top: 4px; }

/* ---------- Exam Specific ---------- */
.exam-timer {
  position: sticky; top: var(--nav-height); z-index: 50;
  background: rgba(255, 255, 255, .8); backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border-radius: var(--radius); padding: 12px 24px;
  box-shadow: var(--shadow); display: flex; justify-content: space-between;
  align-items: center; margin-bottom: 18px;
  border: 1px solid rgba(228, 233, 240, .6);
}
.timer-value {
  font-size: 1.4em; font-weight: 800; color: var(--brand-primary);
  font-variant-numeric: tabular-nums;
}
.timer-value.warn { color: var(--error); animation: blink 1s infinite; }
@keyframes blink { 50% { opacity: .4; } }
.palette {
  display: grid; grid-template-columns: repeat(5, 1fr); gap: 6px;
}
.pal-btn {
  aspect-ratio: 1; border: 1.5px solid var(--border); border-radius: var(--radius-sm);
  background: var(--card); font-size: .78em; font-weight: 600;
  cursor: pointer; transition: all .15s; display: flex;
  align-items: center; justify-content: center; color: var(--text);
}
.pal-btn:hover { border-color: var(--brand-primary); color: var(--brand-primary); }
.pal-btn.current {
  border-color: var(--brand-accent); background: var(--warning-bg);
  font-weight: 800; color: var(--brand-accent);
}
.pal-btn.done {
  background: var(--brand-primary); color: #fff; border-color: var(--brand-primary);
}

/* ---------- Exam Layout ---------- */
.exam-layout { display: none; gap: 20px; }
.exam-layout.active { display: grid; grid-template-columns: 1fr 180px; }
.exam-sidebar { position: sticky; top: calc(var(--nav-height) + 80px); align-self: start; }
.exam-sidebar .card { padding: 18px; }

/* ---------- Answer Palette (Practice & Exam) ---------- */
.answer-palette {
  display: flex; flex-wrap: wrap; gap: 8px;
  padding: 16px 0; margin-top: 12px;
  border-top: 1px solid var(--border);
}
.palette-item {
  width: 36px; height: 36px;
  display: flex; align-items: center; justify-content: center;
  border-radius: var(--radius-sm); font-size: 0.85em; font-weight: 600;
  border: 1.5px solid var(--border); background: var(--card);
  cursor: pointer; transition: all .2s; color: var(--text-secondary);
}
.palette-item:hover { border-color: var(--brand-primary); color: var(--brand-primary); }
.palette-item.current {
  border-color: var(--brand-accent); background: var(--warning-bg);
  color: var(--brand-accent); font-weight: 800;
}
.palette-item.correct {
  background: var(--success); color: #fff; border-color: var(--success);
}
.palette-item.wrong {
  background: var(--error); color: #fff; border-color: var(--error);
}
.palette-item.answered {
  background: var(--brand-primary); color: #fff; border-color: var(--brand-primary);
}

/* ---------- Start Screen ---------- */
.start-screen { text-align: center; max-width: 560px; margin: 32px auto; }
.start-screen .card { padding: 44px 36px; }
.start-screen h2 {
  color: var(--brand-primary); font-size: 1.55em; margin-bottom: 8px;
  font-weight: 800;
}
.rules {
  text-align: left; background: #F8F9FF; border-radius: var(--radius);
  padding: 22px 28px; margin: 22px 0;
  border-left: 4px solid var(--brand-primary);
}
.rules li { margin: 6px 0; font-size: .9em; padding-left: 4px; }

/* ---------- Results Screen ---------- */
.results { display: none; max-width: 680px; margin: 0 auto; }
.results.active { display: block; }
.results-header { text-align: center; padding: 40px; }
.results-header h2 { color: var(--brand-primary); margin-bottom: 4px; font-weight: 800; }
.score-big {
  font-size: 3.2em; font-weight: 800; color: var(--brand-primary);
  margin: 14px 0;
}
.results-detail { color: var(--text-secondary); font-size: .9em; }
.breakdown-item {
  display: flex; align-items: center; gap: 10px;
  padding: 9px 0; border-bottom: 1px solid #F0F2F5; font-size: .85em;
}
.breakdown-item:last-child { border-bottom: none; }
.breakdown-num {
  width: 28px; height: 28px; border-radius: 50%; display: flex;
  align-items: center; justify-content: center;
  font-size: .72em; font-weight: 700; color: #fff; flex-shrink: 0;
}
.breakdown-num.correct { background: var(--success); }
.breakdown-num.wrong { background: var(--error); }
.breakdown-num.skipped { background: #B0B8C4; }

/* ---------- Review Page ---------- */
.review-filters { display: flex; gap: 8px; margin-bottom: 16px; flex-wrap: wrap; }
.review-empty { text-align: center; padding: 52px; color: var(--text-secondary); }
.review-empty .empty-icon { font-size: 3em; margin-bottom: 12px; }

/* ---------- Chart / Radar ---------- */
.radar-wrap { display: flex; justify-content: center; padding: 16px 0; }

/* ---------- XP / Level Bar ---------- */
.xp-bar { margin: 16px 0; }
.xp-bar-label {
  display: flex; justify-content: space-between;
  font-size: .78em; color: var(--text-secondary); margin-bottom: 4px;
}
.xp-track { height: 8px; background: #E4E9F0; border-radius: 4px; overflow: hidden; }
.xp-fill {
  height: 100%; background: linear-gradient(90deg, var(--brand-primary), var(--brand-primary-light));
  border-radius: 4px; transition: width .5s;
}

/* ---------- Footer ---------- */
.footer {
  text-align: center; padding: 32px 0;
  color: var(--text-secondary); font-size: .78em; margin-top: 24px;
}

/* ---------- Animations ---------- */
@keyframes slideIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
@keyframes popIn {
  0% { transform: scale(.85); opacity: 0; }
  100% { transform: scale(1); opacity: 1; }
}
.animate-in { animation: slideIn .35s ease-out; }

/* ---------- Section ---------- */
.section { margin-bottom: 28px; }

/* ---------- Question Title ---------- */
.question-title {
  font-size: 1.05em; font-weight: 600; line-height: 1.8;
  margin-bottom: 16px; color: var(--text);
}

/* ---------- Question Nav ---------- */
.question-nav {
  display: flex; align-items: center; gap: 12px;
  margin-top: 20px; padding-top: 16px;
  border-top: 1px solid var(--border);
}

/* ---------- Practice Nav ---------- */
.practice-count {
  margin-left: auto; font-size: 0.85em;
  color: var(--text-secondary); font-weight: 600;
}

/* ---------- Exam Components ---------- */
.exam-header {
  display: flex; align-items: center; gap: 16px;
  padding: 14px 20px; margin-bottom: 16px;
  background: var(--card); border-radius: var(--radius);
  box-shadow: var(--shadow-sm); border: 1px solid var(--border);
  position: sticky; top: 60px; z-index: 10;
}
.exam-title { font-weight: 700; font-size: 1em; }
.exam-progress { font-size: 0.85em; color: var(--text-secondary); font-weight: 600; }
.exam-timer {
  margin-left: auto; font-size: 1.15em; font-weight: 800;
  color: var(--brand-primary); background: var(--bg-secondary);
  padding: 6px 16px; border-radius: 8px; font-family: var(--font-code);
}
.exam-content {
  display: flex; flex-direction: column; gap: 0;
}
.exam-content .answer-palette {
  display: flex; flex-wrap: wrap; gap: 8px;
  padding: 16px 0; margin-top: 12px;
  border-top: 1px solid var(--border);
}
.exam-content .answer-palette .palette-title {
  width: 100%; margin-bottom: 4px;
}
.exam-content .answer-palette .palette-items {
  display: flex; flex-wrap: wrap; gap: 6px;
  width: 100%; margin-bottom: 8px;
}
.exam-content .answer-palette .palette-item { width: 36px; height: 36px; }
.exam-content .answer-palette .exam-progress-bar { width: 100%; margin-bottom: 8px; }
.exam-content .answer-palette .exam-summary {
  width: 100%; text-align: center; margin-bottom: 8px;
}
.exam-content .answer-palette .btn-submit-exam {
  width: auto; margin: 0 auto; padding: 12px 48px;
}
.exam-nav {
  display: flex; align-items: center; gap: 12px;
  margin-top: 20px; padding-top: 16px;
  border-top: 1px solid var(--border);
}
.palette-title {
  font-weight: 700; font-size: 0.85em; margin-bottom: 8px;
  color: var(--text-secondary);
}

/* ---------- Text Utilities ---------- */
.text-success { color: var(--success); }
.text-error { color: var(--error); }
.btn-submit-exam {
  width: 100%; padding: 14px 20px; margin-top: 16px;
  background: var(--gradient-brand);
  color: #fff; border: none; border-radius: var(--radius);
  font-size: 0.95em; font-weight: 700; cursor: pointer;
  transition: all 0.3s ease; box-shadow: 0 4px 15px var(--gradient-brand-shadow);
  letter-spacing: 1px;
}
.btn-submit-exam:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(102, 126, 234, 0.45);
}
.btn-submit-exam:active {
  transform: translateY(0);
  box-shadow: 0 2px 8px var(--gradient-brand-shadow);
}
.exam-progress-bar {
  width: 100%; height: 4px; background: var(--border); border-radius: 2px;
  margin-bottom: 12px; overflow: hidden;
}
.exam-progress-fill {
  height: 100%; background: var(--gradient-brand);
  border-radius: 2px; transition: width 0.3s ease;
}
.exam-summary {
  margin-top: 12px; padding: 10px; background: var(--bg-secondary);
  border-radius: var(--radius-sm); font-size: 0.82em; color: var(--text-secondary);
  text-align: center; line-height: 1.6;
}
.exam-summary strong { color: var(--text-primary); }

/* ---------- Utility ---------- */
.hidden { display: none !important; }
.text-center { text-align: center; }
.text-muted { color: var(--text-secondary); }
.mt-sm { margin-top: 8px; }
.mt-md { margin-top: 16px; }
.mb-md { margin-bottom: 16px; }
.flex-center { display: flex; align-items: center; justify-content: center; }

/* ---------- Print ---------- */
@media print {
  .nav, .no-print, .btn, .editor-toolbar { display: none !important; }
  body { background: #fff; font-size: 12px; }
  .page-body { padding-top: 0; }
  .card, .question-card { box-shadow: none; border: 1px solid #ddd; break-inside: avoid; }
}

/* ============================================================
   Auth (Login / Register)
   ============================================================ */
.auth-page {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px;
  background: var(--gradient-brand);
}
.auth-card {
  background: var(--card);
  border-radius: var(--radius-lg);
  padding: 40px 32px;
  width: 100%;
  max-width: 400px;
  box-shadow: var(--shadow-lg);
}
.auth-logo { text-align: center; margin-bottom: 28px; }
.auth-logo h1 { font-size: 1.8em; margin-bottom: 4px; }
.auth-logo .badge { background: var(--brand-primary); color: #fff; padding: 2px 8px; border-radius: var(--radius-sm); font-size: 0.6em; }
.form-group { margin-bottom: 14px; }
.form-input {
  width: 100%;
  padding: 12px 14px;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 15px;
  font-family: var(--font);
  transition: border-color .2s;
  outline: none;
}
.form-input:focus { border-color: var(--brand-primary); box-shadow: 0 0 0 3px rgba(115,88,255,.12); }
.auth-error {
  background: var(--error-bg);
  color: var(--error);
  padding: 10px 12px;
  border-radius: var(--radius-sm);
  font-size: 13px;
  margin-bottom: 12px;
}
.auth-toggle { text-align: center; margin-top: 16px; font-size: 13px; color: var(--text-secondary); }
.auth-toggle a { color: var(--brand-primary); text-decoration: none; font-weight: 600; }

/* ============================================================
   Nav logout
   ============================================================ */
.nav-logout {
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 1.1em;
  padding: 4px 8px;
  border-radius: var(--radius-sm);
  transition: background .2s;
}
.nav-logout:hover { background: rgba(0,0,0,.06); color: var(--error); }

/* ============================================================
   Table (Teacher)
   ============================================================ */
.table-wrap {
  overflow-x: auto;
  background: var(--card);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
}
.data-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
}
.data-table th, .data-table td {
  padding: 12px 16px;
  text-align: left;
  border-bottom: 1px solid var(--border);
}
.data-table th {
  font-weight: 600;
  color: var(--text-secondary);
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: .5px;
  background: var(--bg-secondary);
  position: sticky;
  top: 0;
}
.data-table th:first-child { border-radius: var(--radius) 0 0 0; }
.data-table th:last-child { border-radius: 0 var(--radius) 0 0; }
.data-table tbody tr { transition: background .15s; }
.data-table tbody tr:hover { background: rgba(115,88,255,.04); }
.data-table tbody tr:nth-child(even) { background: rgba(241, 248, 254, .5); }
.data-table tbody tr:nth-child(even):hover { background: rgba(115,88,255,.06); }
.data-table tbody tr:last-child td { border-bottom: none; }
.data-table tbody tr:last-child td:first-child { border-radius: 0 0 0 var(--radius); }
.data-table tbody tr:last-child td:last-child { border-radius: 0 0 var(--radius) 0; }

/* ============================================================
   Top list / Weak list
   ============================================================ */
.top-list, .weak-list { display: flex; flex-direction: column; gap: 8px; }
.top-item, .weak-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 14px;
  background: var(--card);
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-sm);
  font-size: 14px;
}
.top-rank { font-weight: 700; color: var(--brand-primary); min-width: 30px; }
.top-score { margin-left: auto; font-weight: 700; color: var(--success); }
.weak-bar { flex: 1; height: 8px; background: var(--border); border-radius: 4px; overflow: hidden; }
.weak-fill { height: 100%; background: var(--error); border-radius: 4px; transition: width .4s; }

/* ============================================================
   Exam History
   ============================================================ */
.exam-history { display: flex; flex-direction: column; gap: 6px; }
.exam-history-item {
  display: flex;
  gap: 16px;
  padding: 10px 14px;
  background: var(--card);
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-sm);
  font-size: 14px;
}

/* ============================================================
   Q source badge
   ============================================================ */
.q-source {
  background: #e8f5e9;
  color: #2e7d32;
  padding: 2px 8px;
  border-radius: var(--radius-sm);
  font-size: 12px;
  font-weight: 600;
}
.q-kp {
  background: var(--purple-bg);
  color: var(--brand-primary);
  padding: 2px 8px;
  border-radius: var(--radius-sm);
  font-size: 12px;
  font-weight: 600;
}

/* ============================================================
   Exam Detail (post-exam review)
   ============================================================ */
.exam-detail-item {
  background: var(--card);
  border-radius: var(--radius);
  padding: 16px 20px;
  margin-bottom: 12px;
  box-shadow: var(--shadow-sm);
  border-left: 4px solid var(--border);
}
.exam-detail-item.correct { border-left-color: var(--success); }
.exam-detail-item.incorrect { border-left-color: var(--error); }
.exam-detail-header {
  display: flex;
  justify-content: space-between;
  font-size: 13px;
  font-weight: 600;
  margin-bottom: 8px;
}
.exam-detail-title { font-size: 15px; margin-bottom: 8px; }
.exam-detail-options { display: flex; flex-direction: column; gap: 4px; margin-bottom: 8px; }
.exam-opt { padding: 4px 10px; border-radius: var(--radius-sm); font-size: 13px; background: #f8f9fa; }
.exam-opt.answer { background: var(--success-bg); color: var(--success); font-weight: 600; }
.exam-opt.wrong { background: var(--error-bg); color: var(--error); text-decoration: line-through; }
.exam-detail-explain { font-size: 13px; color: var(--text-secondary); background: #f8f9fa; padding: 8px 12px; border-radius: var(--radius-sm); }

/* ============================================================
   Wrong count badge
   ============================================================ */
.wrong-count {
  background: var(--error-bg);
  color: var(--error);
  padding: 2px 10px;
  border-radius: var(--radius-pill);
  font-size: 13px;
  font-weight: 600;
  margin-left: 8px;
}

/* ============================================================
   Review empty
   ============================================================ */
.review-empty {
  text-align: center;
  padding: 60px 20px;
}
.review-empty .empty-icon { font-size: 3em; margin-bottom: 12px; }

/* ============================================================
   Paper Selection (Exam)
   ============================================================ */
.paper-list { margin-top: 24px; }
.paper-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
}
.paper-card {
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  cursor: pointer;
  transition: all 0.2s;
}
.paper-card:hover {
  border-color: var(--brand-primary);
  box-shadow: 0 4px 12px rgba(115, 88, 255, 0.15);
  transform: translateY(-2px);
}
.paper-card.random {
  background: var(--gradient-brand);
  color: #fff;
  border: none;
}
.paper-card.random .paper-desc { color: rgba(255,255,255,0.8); }
.paper-card.random:hover { box-shadow: 0 6px 20px rgba(115, 88, 255, 0.3); }
.paper-title {
  font-size: 1.1em;
  font-weight: 700;
  margin-bottom: 8px;
}
.paper-desc {
  font-size: 0.9em;
  margin-bottom: 12px;
}
.paper-info {
  display: flex;
  gap: 16px;
  font-size: 0.85em;
  color: var(--text-secondary);
}
.paper-card.random .paper-info { color: rgba(255,255,255,0.7); }

/* ============================================================
   Student Cards (Teacher)
   ============================================================ */
.section-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: 16px;
}
.section-header .section-title { margin-bottom: 0; }
.section-actions { display: flex; gap: 8px; }
.student-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 16px;
}
.stu-card {
  background: var(--card);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  cursor: pointer;
  transition: all 0.2s;
}
.stu-card:hover {
  border-color: var(--brand-primary);
  box-shadow: 0 4px 16px rgba(115,88,255,.12);
  transform: translateY(-2px);
}
.stu-card-head {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 14px;
}
.stu-avatar {
  width: 48px; height: 48px;
  border-radius: 50%;
  background: var(--gradient-brand);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.2em;
  font-weight: 700;
  flex-shrink: 0;
}
.stu-info { flex: 1; min-width: 0; }
.stu-name { font-weight: 700; font-size: 1.05em; }
.stu-id { font-size: 0.82em; color: var(--text-secondary); }
.stu-actions { display: flex; gap: 4px; }
.btn-icon {
  background: none; border: none; cursor: pointer;
  font-size: 1.1em; padding: 4px 6px; border-radius: var(--radius-sm);
  transition: background 0.2s;
}
.btn-icon:hover { background: var(--bg); }
.btn-danger-icon:hover { background: var(--error-bg); }
.stu-stats-row {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  text-align: center;
  margin-bottom: 10px;
}
.stu-stat-val { display: block; font-weight: 700; font-size: 1.1em; }
.stu-stat-lbl { font-size: 0.75em; color: var(--text-secondary); }
.stu-tag {
  display: inline-block;
  background: var(--brand-light);
  color: var(--brand-primary);
  padding: 2px 10px;
  border-radius: var(--radius-pill);
  font-size: 0.8em;
  margin-bottom: 6px;
}
.stu-last { font-size: 0.8em; color: var(--text-secondary); }

/* ============================================================
   Modal
   ============================================================ */
#modalOverlay {
  display: none;
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  z-index: 1000;
  align-items: center;
  justify-content: center;
  padding: 20px;
}
#modalOverlay.show {
  display: flex;
  animation: fadeIn .2s ease-out;
}
.modal-mask {
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  background: rgba(0,0,0,.45);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
}
.modal-content {
  position: relative;
  background: var(--card);
  border-radius: var(--radius-lg);
  width: 100%;
  max-width: 500px;
  max-height: 85vh;
  overflow-y: auto;
  box-shadow: 0 20px 60px rgba(0,0,0,.2);
  z-index: 1;
  animation: popIn .25s ease-out;
}
.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 24px 0;
}
.modal-header h3 {
  font-size: 1.1em;
  font-weight: 700;
  color: var(--text);
  margin: 0;
}
.modal-close {
  width: 32px; height: 32px;
  display: flex; align-items: center; justify-content: center;
  border: none; background: var(--bg-secondary);
  border-radius: 50%; cursor: pointer;
  font-size: 1.1em; color: var(--text-secondary);
  transition: all .2s; flex-shrink: 0;
}
.modal-close:hover { background: var(--error-bg); color: var(--error); }
.modal-body {
  padding: 16px 24px;
}
.modal-footer {
  display: flex;
  justify-content: flex-end;
  gap: 10px;
  padding: 0 24px 20px;
}
.form-label {
  display: block;
  font-size: 13px;
  font-weight: 600;
  margin-bottom: 4px;
  color: var(--text-secondary);
}

/* ============================================================
   Student Profile
   ============================================================ */
.profile-header {
  display: flex;
  align-items: center;
  gap: 20px;
  padding: 24px;
  background: var(--card);
  border-radius: var(--radius-lg);
  border: 1.5px solid var(--border);
  margin-top: 16px;
}
.profile-avatar {
  width: 72px; height: 72px;
  border-radius: 50%;
  background: var(--gradient-brand);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2em;
  font-weight: 700;
  flex-shrink: 0;
}
.profile-info h2 { margin: 0 0 6px; font-size: 1.3em; }
.profile-info p { margin: 2px 0; font-size: 0.9em; color: var(--text-secondary); }

/* ============================================================
   Daily Chart
   ============================================================ */
.daily-chart {
  display: flex;
  align-items: flex-end;
  gap: 6px;
  height: 120px;
  padding: 16px 8px 0;
  overflow-x: auto;
}
.daily-bar-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  flex: 1;
  min-width: 32px;
}
.daily-bar {
  width: 100%;
  max-width: 28px;
  background: var(--gradient-brand);
  border-radius: 4px 4px 0 0;
  transition: height 0.3s;
}
.daily-label {
  font-size: 0.7em;
  color: var(--text-secondary);
  white-space: nowrap;
}

/* ============================================================
   Wrong List (Profile)
   ============================================================ */
.wrong-list { display: flex; flex-direction: column; gap: 12px; }
.wrong-item {
  background: var(--bg);
  border-radius: var(--radius);
  padding: 14px;
  border-left: 3px solid var(--error);
}
.wrong-q { font-weight: 600; margin-bottom: 6px; font-size: 0.95em; }
.wrong-detail { display: flex; gap: 16px; font-size: 0.85em; }

/* ============================================================
   Batch Result
   ============================================================ */
.batch-result { text-align: center; }
.batch-list { display: flex; flex-wrap: wrap; gap: 6px; justify-content: center; margin-top: 8px; }
.batch-item {
  background: var(--bg);
  padding: 4px 10px;
  border-radius: var(--radius-pill);
  font-size: 0.85em;
}

/* ============================================================
   Rank Table (Teacher Dashboard)
   ============================================================ */
.rank-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
  background: var(--card);
  border-radius: var(--radius);
  overflow: hidden;
  border: 1px solid var(--border);
}
.rank-table th, .rank-table td {
  padding: 10px 14px;
  text-align: left;
  border-bottom: 1px solid var(--border);
}
.rank-table th {
  background: var(--bg-secondary);
  font-weight: 600;
  color: var(--text-secondary);
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: .5px;
}
.rank-table tbody tr:last-child td { border-bottom: none; }
.rank-table tbody tr:nth-child(even) { background: rgba(241, 248, 254, .5); }
.rank-table tbody tr:hover { background: rgba(115,88,255,.04); }
.rank-num {
  width: 28px; height: 28px; border-radius: 50%; display: inline-flex;
  align-items: center; justify-content: center;
  font-size: .78em; font-weight: 700; color: #fff; flex-shrink: 0;
}
.rank-num.gold { background: linear-gradient(135deg, #FFD700, #FFA000); }
.rank-num.silver { background: linear-gradient(135deg, #C0C0C0, #9E9E9E); }
.rank-num.bronze { background: linear-gradient(135deg, #CD7F32, #A0522D); }
.rank-num.normal { background: var(--text-secondary); }
.rank-score { font-weight: 700; color: var(--brand-primary); }
.rank-exams { color: var(--text-secondary); font-size: .85em; }

/* ============================================================
   Radar Chart (SVG)
   ============================================================ */
.radar-chart {
  display: flex; justify-content: center; align-items: center;
  padding: 20px; background: var(--card);
  border-radius: var(--radius); border: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
}
.radar-chart svg { max-width: 340px; width: 100%; height: auto; }
.radar-grid { fill: none; stroke: var(--border); stroke-width: 1; }
.radar-axis { stroke: var(--border); stroke-width: 0.5; }
.radar-area {
  fill: rgba(115, 88, 255, .15); stroke: var(--brand-primary);
  stroke-width: 2; transition: all .3s;
}
.radar-area:hover { fill: rgba(115, 88, 255, .25); }
.radar-dot {
  fill: var(--brand-primary); stroke: #fff; stroke-width: 2;
  transition: r .2s;
}
.radar-dot:hover { r: 5; }
.radar-label {
  font-size: 11px; fill: var(--text-secondary); font-weight: 600;
  text-anchor: middle;
}
.radar-value {
  font-size: 10px; fill: var(--brand-primary); font-weight: 700;
  text-anchor: middle;
}

/* ============================================================
   Trend Chart (SVG Line)
   ============================================================ */
.trend-chart {
  background: var(--card); border-radius: var(--radius);
  border: 1px solid var(--border); box-shadow: var(--shadow-sm);
  padding: 20px; overflow-x: auto;
}
.trend-chart svg { min-width: 300px; width: 100%; height: auto; }
.trend-line { fill: none; stroke: var(--brand-primary); stroke-width: 2.5; stroke-linecap: round; stroke-linejoin: round; }
.trend-area { fill: url(#trendGradient); opacity: .3; }
.trend-dot { fill: var(--brand-primary); stroke: #fff; stroke-width: 2; }
.trend-grid { stroke: var(--border); stroke-width: .5; stroke-dasharray: 4 4; }
.trend-label { font-size: 11px; fill: var(--text-secondary); }
.trend-axis-label { font-size: 10px; fill: var(--text-secondary); font-weight: 600; }

/* ============================================================
   Accuracy Overlay Chart
   ============================================================ */
.accuracy-chart {
  background: var(--card); border-radius: var(--radius);
  border: 1px solid var(--border); box-shadow: var(--shadow-sm);
  padding: 20px; overflow-x: auto;
}
.accuracy-chart svg { min-width: 300px; width: 100%; height: auto; }
.accuracy-bar { fill: var(--brand-primary); opacity: .6; rx: 3; }
.accuracy-bar:hover { opacity: .8; }
.accuracy-line { fill: none; stroke: var(--brand-accent); stroke-width: 2.5; stroke-linecap: round; stroke-linejoin: round; }
.accuracy-dot { fill: var(--brand-accent); stroke: #fff; stroke-width: 2; }

/* ============================================================
   Dashboard Section Grid
   ============================================================ */
.dashboard-grid {
  display: grid; grid-template-columns: 1fr 1fr;
  gap: 16px; margin-bottom: 28px;
}
.dashboard-grid .section { margin-bottom: 0; }
.dashboard-grid .section-title { margin-bottom: 12px; }

/* ============================================================
   Three-way Responsive: Tablet (768px)
   ============================================================ */
@media (max-width: 1024px) and (min-width: 641px) {
  .nav { padding: 10px 16px; }
  .nav-links a { padding: 8px 12px; font-size: 14px; }
  .hero { padding: 32px 24px; }
  .kp-grid { grid-template-columns: repeat(3, 1fr); gap: 14px; }
  .student-grid { grid-template-columns: repeat(2, 1fr); }
  .stats-grid { grid-template-columns: repeat(3, 1fr); gap: 14px; }
  .profile-header { gap: 16px; padding: 20px; }
  .profile-avatar { width: 64px; height: 64px; font-size: 1.7em; }
  .modal-content { max-width: 560px; padding: 28px; }
  .daily-chart { height: 140px; }
}

/* ============================================================
   Three-way Responsive: Mobile (640px)
   ============================================================ */
@media (max-width: 640px) {
  /* Nav mobile */
  .nav { flex-wrap: wrap; padding: 10px 12px; gap: 6px; }
  .nav-brand span { display: none; }
  .nav-links { gap: 2px; width: 100%; justify-content: center; }
  .nav-links a { padding: 8px 10px; font-size: 13px; min-height: 36px; }
  .nav-user { font-size: 13px; }
  .nav-user span { display: none; }
  .nav-user .xp-badge { display: none; }

  /* Hero mobile */
  .hero { padding: 24px 16px; }
  .hero h1 { font-size: 1.2em; }
  .hero p { font-size: 0.9em; }

  /* Knowledge points mobile */
  .kp-grid { grid-template-columns: repeat(2, 1fr); gap: 10px; }
  .kp-card { padding: 14px 10px; }
  .kp-card .num { font-size: 1em; }
  .kp-card .title { font-size: 0.82em; }

  /* Quick actions mobile */
  .quick-actions { grid-template-columns: 1fr; gap: 10px; }
  .quick-actions a { padding: 14px; font-size: 14px; }

  /* Stats mobile */
  .stats-grid { grid-template-columns: repeat(2, 1fr); gap: 8px; }
  .stat-card { padding: 12px 8px; }
  .stat-value { font-size: 1.3em; }

  /* Practice mobile */
  .question-card { padding: 16px; margin: 0 12px; }
  .question-card .q-title { font-size: 15px; line-height: 1.5; }
  .option { padding: 14px 12px; font-size: 14px; min-height: 48px; }
  .option:active { transform: scale(0.98); }
  .q-nav { flex-direction: column; gap: 8px; }
  .q-nav .btn { width: 100%; }
  .q-pager { flex-wrap: wrap; gap: 6px; justify-content: center; }
  .q-pager span { width: 32px; height: 32px; font-size: 12px; }
  .answer-palette { gap: 6px; padding: 12px 0; }
  .palette-item { width: 32px; height: 32px; font-size: 0.8em; }
  .filter-tabs { margin-left: 0; margin-top: 8px; width: 100%; }

  /* Mock exam mobile */
  .exam-header { flex-direction: row; flex-wrap: wrap; gap: 8px; padding: 12px; position: relative; top: auto; }
  .exam-layout.active { grid-template-columns: 1fr; }
  .exam-sidebar { position: static; }
  .palette { grid-template-columns: repeat(10, 1fr); }
  .exam-content .answer-palette .palette-items { gap: 4px; }
  .exam-content .answer-palette .palette-item { width: 32px; height: 32px; font-size: 0.8em; }
  .exam-content .answer-palette .btn-submit-exam { margin-top: 8px; padding: 12px; }
  .exam-content .answer-palette .exam-progress-bar { width: 100%; }
  .exam-content .answer-palette .exam-summary { width: 100%; margin-top: 4px; }

  /* Auth mobile */
  .auth-card { padding: 28px 20px; }
  .auth-logo h1 { font-size: 1.4em; }

  /* Teacher mobile */
  .student-grid { grid-template-columns: 1fr; gap: 12px; }
  .stu-card { padding: 16px; }
  .stu-card-head { gap: 10px; }
  .stu-avatar { width: 42px; height: 42px; font-size: 1em; }
  .stu-stats-row { gap: 4px; }
  .stu-stat-val { font-size: 1em; }
  .section-header { flex-direction: column; align-items: flex-start; }
  .section-actions { width: 100%; }
  .section-actions .btn { flex: 1; font-size: 13px; padding: 10px; }
  .teacher-stats { grid-template-columns: repeat(3, 1fr); gap: 8px; }
  .teacher-stat { padding: 10px; }

  /* Profile mobile */
  .profile-header { flex-direction: column; text-align: center; padding: 20px 16px; gap: 12px; }
  .profile-avatar { width: 60px; height: 60px; font-size: 1.5em; }
  .profile-info h2 { font-size: 1.15em; }

  /* Wrong list mobile */
  .wrong-detail { flex-direction: column; gap: 4px; }
  .top-item, .weak-item { padding: 8px 10px; font-size: 13px; }

  /* Daily chart mobile */
  .daily-chart { height: 100px; gap: 4px; padding: 12px 4px 0; }
  .daily-bar-wrap { min-width: 24px; }

  /* Modal mobile */
  .modal-content { margin: 10px; max-height: 90vh; }
  .modal-header { padding: 16px 16px 0; }
  .modal-body { padding: 12px 16px; }
  .modal-footer { padding: 0 16px 16px; }

  /* Paper mobile */
  .paper-grid { grid-template-columns: 1fr; gap: 12px; }
  .paper-card { padding: 16px; }

  /* Button mobile */
  .btn { padding: 12px 20px; font-size: 14px; min-height: 44px; }
  .btn-sm { padding: 8px 14px; font-size: 13px; min-height: 36px; }

  /* Table mobile */
  .data-table { font-size: 12px; }
  .data-table th, .data-table td { padding: 8px 10px; }

  /* Dashboard grid mobile */
  .dashboard-grid { grid-template-columns: 1fr; gap: 12px; }
  .rank-table { font-size: 12px; }
  .rank-table th, .rank-table td { padding: 8px 10px; }
  .radar-chart svg { max-width: 260px; }
  .radar-label { font-size: 9px; }
  .radar-value { font-size: 8px; }
}

/* ============================================================
   Touch-friendly (all screens)
   ============================================================ */
@media (hover: none) and (pointer: coarse) {
  .option { min-height: 48px; }
  .btn { min-height: 44px; }
  .nav-links a { min-height: 40px; display: flex; align-items: center; }
  .stu-card { -webkit-tap-highlight-color: transparent; }
  .btn-icon { font-size: 1.2em; padding: 6px 8px; }
}