/* Header */
.site-header {
  position: sticky; top: 0; z-index: 50;
  background: rgba(255, 255, 255, 0.92); backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--color-border);
}
.header-inner {
  max-width: var(--container); margin: 0 auto; height: var(--header-h);
  padding: 0 var(--space-5); display: flex; align-items: center; gap: var(--space-6);
}
.brand { display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 18px; color: var(--color-text); text-decoration: none; }
.brand:hover { color: var(--color-text); text-decoration: none; }
.brand-mark {
  width: 30px; height: 30px; border-radius: 8px; background: var(--color-primary);
  color: #fff; display: flex; align-items: center; justify-content: center; font-weight: 800; font-size: 16px;
}
.primary-nav { display: flex; gap: 4px; align-items: center; flex: 1; }
.primary-nav a {
  padding: 8px 14px; border-radius: var(--radius); color: var(--color-text-muted); font-weight: 500; font-size: 14px;
  text-decoration: none; transition: background var(--transition), color var(--transition);
}
.primary-nav a:hover { background: var(--color-bg-sub); color: var(--color-text); text-decoration: none; }
.primary-nav a[aria-current="page"] { background: var(--color-bg-sub); color: var(--color-primary); }
.header-actions { display: flex; gap: 8px; align-items: center; }
.nav-toggle { display: none; }
@media (max-width: 720px) {
  .primary-nav {
    position: fixed; top: var(--header-h); left: 0; right: 0; flex-direction: column; align-items: stretch;
    background: #fff; border-bottom: 1px solid var(--color-border); padding: var(--space-4);
    transform: translateY(-110%); transition: transform var(--transition); gap: 0;
  }
  .primary-nav[data-open="true"] { transform: translateY(0); }
  .primary-nav a { padding: 12px 14px; }
  .nav-toggle {
    display: inline-flex; width: 40px; height: 40px; align-items: center; justify-content: center;
    background: transparent; border: 1px solid var(--color-border); border-radius: var(--radius);
  }
  .nav-toggle::before {
    content: ''; width: 18px; height: 2px; background: var(--color-text);
    box-shadow: 0 -6px 0 var(--color-text), 0 6px 0 var(--color-text);
  }
}

/* Main */
.site-main { min-height: calc(100vh - var(--header-h) - 200px); padding: var(--space-8) 0; }
.site-main:focus { outline: none; }
.container { max-width: var(--container); margin: 0 auto; padding: 0 var(--space-5); }

/* Hero */
.hero {
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-2));
  color: #fff; border-radius: var(--radius-xl); padding: var(--space-12) var(--space-8);
  margin-bottom: var(--space-8); box-shadow: var(--shadow);
}
.hero h1 { color: #fff; font-size: 40px; margin-bottom: 12px; letter-spacing: -0.02em; }
.hero p { font-size: 17px; opacity: 0.9; max-width: 600px; margin-bottom: var(--space-6); }
.hero-meta { display: flex; gap: var(--space-6); flex-wrap: wrap; opacity: 0.9; font-size: 14px; }
.hero-meta strong { color: #fff; font-size: 22px; display: block; }
.hero-cta { display: flex; gap: 12px; flex-wrap: wrap; }
.hero-cta .btn-primary { background: #fff; color: var(--color-primary); border-color: #fff; }
.hero-cta .btn-primary:hover { background: var(--color-bg-sub); color: var(--color-primary); }
.hero-cta .btn-outline { color: #fff; border-color: rgba(255,255,255,0.5); }
.hero-cta .btn-outline:hover { background: rgba(255,255,255,0.1); border-color: #fff; color: #fff; }
@media (max-width: 640px) { .hero { padding: var(--space-8) var(--space-5); } .hero h1 { font-size: 30px; } }

/* Grids */
.grid { display: grid; gap: var(--space-5); }
.grid-3 { grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); }
.grid-2 { grid-template-columns: repeat(auto-fill, minmax(360px, 1fr)); }

/* Category rail */
.category-rail {
  display: flex; gap: 8px; overflow-x: auto; padding-bottom: 4px;
  margin-bottom: var(--space-6); -webkit-overflow-scrolling: touch;
}
.category-rail button {
  padding: 8px 16px; border-radius: 999px; border: 1px solid var(--color-border-strong);
  background: #fff; color: var(--color-text); font-weight: 500; font-size: 14px;
  white-space: nowrap; flex: 0 0 auto;
}
.category-rail button[aria-pressed="true"] { background: var(--color-primary); border-color: var(--color-primary); color: #fff; }

/* Product card */
.product-card { display: flex; flex-direction: column; gap: var(--space-3); }
.product-card .badge-row { display: flex; gap: 6px; flex-wrap: wrap; }
.product-card h3 { font-size: 19px; }
.product-card .desc { color: var(--color-text-muted); font-size: 14px; }
.product-card .metrics { display: flex; gap: var(--space-5); padding-top: var(--space-3); border-top: 1px solid var(--color-border); margin-top: auto; }
.product-card .metrics div { flex: 1; }
.product-card .metrics .v { font-weight: 700; font-size: 18px; color: var(--color-text); }
.product-card .metrics .l { font-size: 11px; color: var(--color-text-muted); text-transform: uppercase; letter-spacing: 0.05em; }
.product-card .cta-row { display: flex; gap: 8px; padding-top: var(--space-3); }

/* Course workspace */
.workspace-header { padding-bottom: var(--space-6); border-bottom: 1px solid var(--color-border); margin-bottom: var(--space-6); }
.workspace-header h1 { font-size: 26px; margin-bottom: 4px; }
.workspace-header .desc { color: var(--color-text-muted); }
.function-tabs { display: flex; gap: 0; border-bottom: 1px solid var(--color-border); margin-bottom: var(--space-6); overflow-x: auto; }
.function-tabs button {
  padding: 12px 20px; border: 0; background: transparent; border-bottom: 2px solid transparent;
  font-weight: 600; font-size: 14px; color: var(--color-text-muted); white-space: nowrap;
}
.function-tabs button:hover { color: var(--color-text); }
.function-tabs button[aria-selected="true"] { color: var(--color-primary); border-bottom-color: var(--color-primary); }

/* Test session */
.test-layout {
  display: grid; grid-template-columns: 280px 1fr; gap: var(--space-6);
}
@media (max-width: 900px) { .test-layout { grid-template-columns: 1fr; } .test-sidebar { order: -1; } }
.test-sidebar { background: #fff; border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: var(--space-5); }
.test-main { background: #fff; border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: var(--space-6); }
.timer {
  display: flex; align-items: baseline; gap: 8px; padding: var(--space-3) var(--space-4);
  background: var(--color-bg-sub); border-radius: var(--radius); margin-bottom: var(--space-4);
}
.timer-time { font-family: var(--font-mono); font-size: 28px; font-weight: 700; color: var(--color-primary); letter-spacing: 0.02em; }
.timer[data-warning="true"] .timer-time { color: var(--color-warn); }
.timer[data-critical="true"] { background: var(--color-danger-bg); }
.timer[data-critical="true"] .timer-time { color: var(--color-danger); }
.question-navigator { display: grid; grid-template-columns: repeat(8, 1fr); gap: 4px; margin-top: var(--space-3); }
.question-navigator button {
  aspect-ratio: 1; border-radius: 6px; border: 1px solid var(--color-border); background: #fff;
  font-size: 12px; font-weight: 600; color: var(--color-text-muted); padding: 0;
}
.question-navigator button[data-state="current"] { background: var(--color-accent); color: #fff; border-color: var(--color-accent); }
.question-navigator button[data-state="answered"] { background: var(--color-success); color: #fff; border-color: var(--color-success); }
.question-navigator button[data-state="flagged"] { background: var(--color-warn-bg); border-color: var(--color-warn); }
.question-navigator button[data-state="review"] { background: var(--color-warn); color: #fff; border-color: var(--color-warn); }
.question-navigator button[data-section-done="true"]:not([data-state="current"]):not([data-state="answered"]):not([data-state="flagged"]) { opacity: 0.5; }
.test-question { margin-bottom: var(--space-6); }
.test-question .q-meta { display: flex; justify-content: space-between; align-items: center; margin-bottom: var(--space-4); padding-bottom: var(--space-3); border-bottom: 1px solid var(--color-border); }
.test-question .q-tools { display: flex; gap: 4px; }
.test-question .q-choices { display: flex; flex-direction: column; gap: var(--space-3); }
.test-actions { display: flex; justify-content: space-between; padding-top: var(--space-4); border-top: 1px solid var(--color-border); margin-top: var(--space-6); }

/* AST rendering */
.ast { display: block; }
.ast-inline-math { display: inline-block; }
.ast-block-math { display: block; margin: var(--space-3) 0; overflow-x: auto; }
.ast-image { max-width: 100%; border-radius: var(--radius); border: 1px solid var(--color-border); margin: var(--space-3) 0; }
.ast-table { width: 100%; border-collapse: collapse; margin: var(--space-3) 0; font-size: 14px; }
.ast-table th, .ast-table td { padding: 8px 12px; border: 1px solid var(--color-border); }
.ast-table th { background: var(--color-bg-sub); font-weight: 700; }
.ast-svg { background: #fff; border: 1px solid var(--color-border); border-radius: var(--radius); padding: var(--space-3); margin: var(--space-3) 0; }
.ast-svg svg { max-width: 100%; }
.ast-svg-caption { font-size: 12px; color: var(--color-text-muted); text-align: center; margin-top: 6px; }
.ast-callout { padding: 10px 14px; background: var(--color-bg-sub); border-left: 3px solid var(--color-primary); border-radius: 6px; margin: var(--space-3) 0; }

/* Report card */
.score-hero { text-align: center; padding: var(--space-6) 0; }
.score-hero .score { font-size: 56px; font-weight: 800; color: var(--color-primary); letter-spacing: -0.03em; }
.score-hero .pct { font-size: 18px; color: var(--color-text-muted); }
.score-bands { display: grid; grid-template-columns: repeat(auto-fit, minmax(160px, 1fr)); gap: var(--space-3); margin: var(--space-5) 0; }
.score-band { padding: var(--space-4); background: var(--color-bg-sub); border-radius: var(--radius); text-align: center; }
.score-band .v { font-size: 24px; font-weight: 700; color: var(--color-primary); }
.score-band .l { font-size: 12px; color: var(--color-text-muted); text-transform: uppercase; letter-spacing: 0.05em; }

/* Account rail layout */
.account-layout { display: grid; grid-template-columns: 240px 1fr; gap: var(--space-6); }
@media (max-width: 800px) { .account-layout { grid-template-columns: 1fr; } }
.account-rail { background: #fff; border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: var(--space-3); height: max-content; position: sticky; top: calc(var(--header-h) + var(--space-4)); }
.account-rail h4 { font-size: 11px; text-transform: uppercase; letter-spacing: 0.08em; color: var(--color-text-faint); padding: 8px 12px 4px 12px; margin: 0; }
.account-rail a { display: block; padding: 8px 12px; border-radius: 6px; color: var(--color-text); font-size: 14px; text-decoration: none; }
.account-rail a:hover { background: var(--color-bg-sub); text-decoration: none; }
.account-rail a[aria-current="page"] { background: var(--color-bg-sub); color: var(--color-primary); font-weight: 600; }

/* Errors list */
.error-item { padding: var(--space-4); border: 1px solid var(--color-border); border-radius: var(--radius); margin-bottom: var(--space-3); background: #fff; }
.error-item[data-open="true"] { border-color: var(--color-primary); }
.error-item-header { display: flex; align-items: center; gap: 12px; cursor: pointer; }
.error-item-header .num { font-weight: 700; color: var(--color-text-muted); min-width: 32px; }
.error-item-header .preview { flex: 1; font-size: 14px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.error-item-body { padding-top: var(--space-4); margin-top: var(--space-3); border-top: 1px solid var(--color-border); display: none; }
.error-item[data-open="true"] .error-item-body { display: block; }
.error-answer-block { background: var(--color-bg-sub); padding: var(--space-3); border-radius: 6px; margin: var(--space-3) 0; }
.error-answer-block .label { font-size: 11px; text-transform: uppercase; letter-spacing: 0.05em; color: var(--color-text-muted); font-weight: 700; }
.error-answer-block .my { color: var(--color-danger); }
.error-answer-block .correct { color: var(--color-success); }

/* Footer */
.site-footer {
  background: #0f172a; color: #cbd5e1; padding: var(--space-10) 0 var(--space-6) 0; margin-top: var(--space-12);
}
.site-footer .container { display: grid; grid-template-columns: 2fr 1fr 1fr 1fr; gap: var(--space-8); }
@media (max-width: 720px) { .site-footer .container { grid-template-columns: 1fr 1fr; } }
.site-footer h4 { color: #fff; font-size: 13px; text-transform: uppercase; letter-spacing: 0.05em; margin-bottom: var(--space-3); }
.site-footer a { color: #cbd5e1; font-size: 14px; display: block; padding: 4px 0; text-decoration: none; }
.site-footer a:hover { color: #fff; }
.site-footer .legal { grid-column: 1 / -1; padding-top: var(--space-6); margin-top: var(--space-6); border-top: 1px solid #1e293b; font-size: 13px; color: #94a3b8; display: flex; justify-content: space-between; flex-wrap: wrap; gap: var(--space-3); }
.site-footer .brand-block .desc { font-size: 14px; max-width: 280px; margin-top: 8px; }

/* Pagination */
.pagination { display: flex; align-items: center; justify-content: space-between; gap: var(--space-3); padding: var(--space-3) 0; }
.pagination-controls { display: flex; gap: 4px; align-items: center; }
.pagination button { min-width: 36px; padding: 6px 10px; border: 1px solid var(--color-border-strong); background: #fff; border-radius: 6px; font-size: 13px; }
.pagination button[aria-current="page"] { background: var(--color-primary); color: #fff; border-color: var(--color-primary); }
.pagination button:disabled { opacity: 0.4; cursor: not-allowed; }