:root {
  --navy: #14304d;
  --blue: #1d5b9e;
  --blue-light: #eaf2fb;
  --gold: #c8932b;
  --green: #1f7a4d;
  --red: #b3261e;
  --gray-bg: #f5f6f8;
  --border: #d8dee5;
  --text: #1d2630;
  --text-soft: #5b6776;
  --radius: 10px;
  --font-display: "Source Serif Pro", Georgia, serif;
  --font-body: "Inter", "Segoe UI", Arial, sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: var(--font-body);
  background: var(--gray-bg);
  color: var(--text);
  line-height: 1.55;
}

.page { display: none; }
.page.active { display: block; }

/* ---------- Login & Rules ---------- */
.login-container, .rules-container {
  max-width: 640px;
  margin: 48px auto;
  background: #fff;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  box-shadow: 0 8px 24px rgba(20, 48, 77, 0.08);
  overflow: hidden;
}

.login-header, .rules-header, .question-header, .closing-header {
  background: linear-gradient(135deg, var(--navy), var(--blue));
  color: #fff;
  padding: 28px 32px;
  text-align: center;
}

.header-logo { margin-bottom: 10px; }
.header-logo .logo { height: 48px; }

.login-header h1, .rules-header h1, .question-header h1, .closing-header h1 {
  font-family: var(--font-display);
  font-size: 1.45rem;
  margin: 0 0 4px;
}
.login-header h2, .rules-header h2, .question-header h2, .closing-header h2 { font-size: 1rem; font-weight: 500; margin: 2px 0; opacity: .92; }
.login-header h3, .rules-header h3, .question-header h3 { font-size: .88rem; font-weight: 400; margin: 2px 0; opacity: .8; }
.login-header p, .rules-header p, .question-header p { font-size: .85rem; margin: 8px 0 0; opacity: .85; }

.login-form, .rules-content { padding: 28px 32px 32px; }

.form-group { margin-bottom: 18px; }
.form-group label { display: block; font-weight: 600; margin-bottom: 6px; font-size: .92rem; }
.form-group input[type="text"],
.form-group input[type="number"],
.form-group textarea,
.form-group select {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 6px;
  font-size: .95rem;
  font-family: inherit;
}
.form-group small { color: var(--text-soft); font-size: .8rem; }

button {
  cursor: pointer;
  font-family: inherit;
  border: none;
  border-radius: 6px;
}

.login-form button, .btn-start-exam, .btn-home {
  width: 100%;
  background: var(--blue);
  color: #fff;
  padding: 13px;
  font-size: 1rem;
  font-weight: 600;
  margin-top: 6px;
}
.login-form button:hover, .btn-start-exam:hover { background: var(--navy); }

.rules-content h3 { color: var(--navy); margin-top: 22px; }
.rules-content ul { padding-left: 20px; }
.rules-content li { margin-bottom: 6px; }

.warning-box {
  background: #fff7e6;
  border: 1px solid var(--gold);
  border-radius: 8px;
  padding: 14px 18px;
  margin: 20px 0;
}
.warning-box h4 { margin: 0 0 6px; color: #8a6512; }
.warning-box p { margin: 0; font-size: .9rem; }

/* ---------- Exam layout ---------- */
#examPage.active { display: flex; min-height: 100vh; }

.sidebar {
  width: 270px;
  flex-shrink: 0;
  background: var(--navy);
  color: #fff;
  padding: 22px 0;
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
}
.sidebar-header { padding: 0 20px 16px; border-bottom: 1px solid rgba(255,255,255,.15); margin-bottom: 12px; }
.sidebar-header h3 { margin: 0 0 10px; font-size: .95rem; opacity: .9; }
.student-info p { margin: 2px 0; font-size: .82rem; opacity: .85; word-break: break-word; }

.sidebar-nav { display: flex; flex-direction: column; }
.sidebar-nav a {
  color: #cfe0f3;
  text-decoration: none;
  padding: 11px 20px;
  font-size: .88rem;
  border-left: 3px solid transparent;
}
.sidebar-nav a:hover { background: rgba(255,255,255,.06); }
.sidebar-nav a.active { background: rgba(255,255,255,.1); color: #fff; border-left-color: var(--gold); font-weight: 600; }
.sidebar-nav a.locked::after { content: " ✓"; color: #7fd99a; }

.main-content { flex: 1; padding: 0; position: relative; }

.mobile-menu-toggle {
  display: none;
  position: fixed;
  top: 14px; left: 14px;
  z-index: 60;
  width: 42px; height: 42px;
  background: var(--navy);
  border-radius: 8px;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
}
.mobile-menu-toggle span { width: 20px; height: 2px; background: #fff; display: block; }

.question-container { display: none; }
.question-container.active { display: block; }

.question-content { max-width: 880px; margin: 0 auto; padding: 28px 30px 60px; }
.question-content h2 { color: var(--navy); font-family: var(--font-display); font-size: 1.5rem; margin-bottom: 4px; }
.question-content h3.theme { color: var(--blue); font-weight: 600; font-size: 1.02rem; margin-top: 0; }

.guide-box {
  background: var(--blue-light);
  border-left: 4px solid var(--blue);
  border-radius: 6px;
  padding: 16px 20px;
  margin: 18px 0;
  font-size: .92rem;
}
.guide-box h4 { margin: 0 0 8px; color: var(--navy); }
.guide-box ol, .guide-box ul { margin: 0; padding-left: 20px; }
.guide-box li { margin-bottom: 5px; }

.example-box {
  background: #f4f9f4;
  border: 1px dashed var(--green);
  border-radius: 6px;
  padding: 14px 18px;
  margin: 16px 0;
  font-size: .88rem;
}
.example-box h4 { margin: 0 0 6px; color: var(--green); }

.data-table, .transport-table, .assignment-table {
  width: 100%;
  border-collapse: collapse;
  margin: 14px 0;
  font-size: .95rem;
}
.data-table th, .data-table td,
.transport-table th, .transport-table td,
.assignment-table th, .assignment-table td {
  border: 1px solid var(--border);
  padding: 10px 12px;
  text-align: center;
}
.assignment-table select {
  font-size: 1rem;
  padding: 9px 10px;
  border: 1px solid var(--border);
  border-radius: 6px;
  min-width: 140px;
  min-height: 42px;
  background: #fff;
}
.data-table th, .transport-table th, .assignment-table th {
  background: var(--navy);
  color: #fff;
  font-weight: 600;
}
.transport-table .stage-label { background: #f0f3f7; font-weight: 600; text-align: left; }

.cell-input {
  width: 64px;
  padding: 6px;
  text-align: center;
  border: 1px solid var(--border);
  border-radius: 4px;
}
.cell-fixed { color: var(--text-soft); font-size: .8rem; }
.sum-cell { font-weight: 600; background: #fafbfc; }
.sum-ok { color: var(--green); }
.sum-warn { color: var(--red); }

.diagram-wrap { background: #fff; border: 1px solid var(--border); border-radius: 8px; padding: 14px; margin: 16px 0; overflow-x: auto; }
.diagram-wrap svg { display: block; margin: 0 auto; }

.edge-table { width: 100%; border-collapse: collapse; font-size: .95rem; margin: 14px 0; }
.edge-table th, .edge-table td { border: 1px solid var(--border); padding: 9px 12px; text-align: center; }
.edge-table th { background: var(--navy); color: #fff; }
.edge-table tr.selected td { background: #fff4d9; }
.edge-table input[type="number"] { width: 80px; padding: 8px; text-align: center; border: 1px solid var(--border); border-radius: 6px; font-size: 1rem; }
.edge-table input[type="checkbox"] { width: 20px; height: 20px; cursor: pointer; }

.calculation-result {
  background: #eef6ff;
  border-radius: 8px;
  padding: 14px 18px;
  margin: 16px 0;
  font-size: .95rem;
}
.calculation-result h4 { margin: 0 0 6px; color: var(--navy); font-size: .92rem; }
.calculation-result span { font-weight: 700; color: var(--blue); }

.form-group textarea { resize: vertical; min-height: 70px; }

.lock-section {
  margin-top: 24px;
  padding-top: 18px;
  border-top: 1px dashed var(--border);
}
.btn-lock {
  background: var(--gold);
  color: #fff;
  padding: 11px 22px;
  font-weight: 600;
  font-size: .92rem;
}
.btn-lock:disabled { background: #9aa5b1; cursor: not-allowed; }
.lock-status { font-size: .85rem; margin-top: 8px; color: var(--text-soft); }

.navigation-buttons {
  max-width: 880px;
  margin: 0 auto;
  padding: 0 30px 50px;
  display: flex;
  justify-content: space-between;
}
.btn-prev, .btn-next {
  background: var(--blue);
  color: #fff;
  padding: 10px 22px;
  font-weight: 600;
  font-size: .92rem;
}
.btn-prev { background: #7c8896; }

.answer-section { background: #fff; border: 1px solid var(--border); border-radius: 8px; padding: 18px 22px; margin-bottom: 18px; }
.answer-section h3 { color: var(--navy); margin-top: 0; }

.print-section { text-align: center; margin: 26px 0 10px; }
.btn-print { background: var(--green); color: #fff; padding: 13px 30px; font-size: 1rem; font-weight: 600; }
.print-warning { font-size: .82rem; color: var(--red); margin-top: 10px; }

.student-info-recap { background: var(--blue-light); border-radius: 8px; padding: 14px 18px; margin-bottom: 18px; }
.student-info-recap p { margin: 3px 0; }

.completion-message { max-width: 560px; margin: 0 auto; padding: 36px 32px; text-align: center; }
.reminder-box { background: #fff7e6; border: 1px solid var(--gold); border-radius: 8px; padding: 16px 20px; margin: 20px 0; text-align: left; }
.btn-home { margin-top: 10px; }

.main-footer { text-align: center; padding: 20px; color: var(--text-soft); font-size: .8rem; }

.sync-badge { display: inline-flex; align-items: center; gap: 6px; font-size: .78rem; padding: 4px 10px; border-radius: 20px; background: #eef6ff; color: var(--blue); margin-left: 8px; }
.sync-badge.ok { background: #eafaf0; color: var(--green); }
.sync-badge.err { background: #fdeceb; color: var(--red); }

.alert {
  position: fixed;
  top: 20px; right: 20px;
  z-index: 200;
  padding: 14px 20px;
  border-radius: 8px;
  color: #fff;
  font-size: .9rem;
  max-width: 320px;
  box-shadow: 0 6px 18px rgba(0,0,0,.18);
}
.alert-error { background: var(--red); }
.alert-success { background: var(--green); }
.alert-info { background: var(--blue); }

/* ---------- Responsive ---------- */
@media (max-width: 880px) {
  .mobile-menu-toggle { display: flex; }
  .sidebar { position: fixed; left: 0; top: 0; transform: translateX(-100%); transition: transform .25s; z-index: 50; width: 250px; }
  .sidebar.mobile-open { transform: translateX(0); }
  #examPage.active { display: block; }
  .question-content, .navigation-buttons { padding-left: 18px; padding-right: 18px; }
  .question-content { padding-top: 64px; }
  .assignment-table select { min-width: 120px; font-size: .95rem; }
  .data-table, .transport-table, .assignment-table, .edge-table { font-size: .85rem; }
  .diagram-wrap { padding: 8px; }
}

/* ---------- Print ---------- */
@media print {
  body * { visibility: hidden; }
  #print-container, #print-container * { visibility: visible; }
  #print-container { position: absolute; left: 0; top: 0; width: 100%; }
}