:root {
  --color-primary: #4f46e5;
  --color-primary-dark: #4338ca;
  --color-secondary: #10b981;
  --color-accent: #f59e0b;
  --color-text: #1f2937;
  --color-text-light: #6b7280;
  --color-bg: #f8fafc;
  --color-bg-card: #ffffff;
  --color-border: #e5e7eb;
  --color-success: #10b981;
  --color-warning: #f59e0b;
  --color-error: #ef4444;
  --color-info: #3b82f6;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --max-width: 1140px;
  --nav-height: 64px;
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  font-family: var(--font-sans);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.6;
  font-size: 16px;
}

a {
  color: var(--color-primary);
  text-decoration: none;
}

a:hover {
  color: var(--color-primary-dark);
  text-decoration: underline;
}

h1,
h2,
h3,
h4 {
  color: var(--color-text);
  line-height: 1.3;
  margin-top: 0;
}

h1 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
}

h2 {
  font-size: 1.5rem;
  margin-bottom: 0.75rem;
}

h3 {
  font-size: 1.2rem;
  margin-bottom: 0.5rem;
}

p {
  margin: 0 0 1rem;
  color: var(--color-text-light);
}

/* ============ 顶部导航 ============ */
.site-nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: #ffffff;
  border-bottom: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
  z-index: 1000;
}

.site-nav .nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 20px;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.site-nav .brand {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--color-primary);
  letter-spacing: 0.5px;
}

.site-nav .brand:hover {
  text-decoration: none;
}

.site-nav .menu {
  display: flex;
  gap: 8px;
  list-style: none;
  margin: 0;
  padding: 0;
}

.site-nav .menu a {
  display: inline-block;
  padding: 8px 14px;
  color: var(--color-text);
  border-radius: var(--radius-sm);
  font-size: 0.95rem;
  transition: background-color 0.15s ease, color 0.15s ease;
}

.site-nav .menu a:hover {
  background: #eef2ff;
  color: var(--color-primary);
  text-decoration: none;
}

.site-nav .menu a.active {
  background: var(--color-primary);
  color: #ffffff;
}

/* ============ 页面主体 ============ */
main.page {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: calc(var(--nav-height) + 32px) 20px 40px;
  min-height: calc(100vh - var(--nav-height));
}

.page-header {
  margin-bottom: 24px;
}

.page-header p {
  margin-top: 6px;
}

.section {
  margin-bottom: 36px;
}

/* ============ 按钮 ============ */
.btn {
  display: inline-block;
  padding: 10px 20px;
  background: var(--color-primary);
  color: #ffffff;
  border: 1px solid var(--color-primary);
  border-radius: var(--radius-sm);
  font-size: 0.95rem;
  cursor: pointer;
  transition: background-color 0.15s ease, transform 0.05s ease;
}

.btn:hover {
  background: var(--color-primary-dark);
  text-decoration: none;
  color: #ffffff;
}

.btn:active {
  transform: translateY(1px);
}

.btn.btn-secondary {
  background: var(--color-secondary);
  border-color: var(--color-secondary);
}

.btn.btn-outline {
  background: transparent;
  color: var(--color-primary);
}

.btn.btn-outline:hover {
  background: var(--color-primary);
  color: #ffffff;
}

/* ============ 卡片 ============ */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 20px;
}

.card {
  background: var(--color-bg-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
  padding: 20px;
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}

.card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.card .card-title {
  margin: 0 0 8px;
  font-size: 1.1rem;
}

.card .card-desc {
  color: var(--color-text-light);
  font-size: 0.9rem;
  margin-bottom: 12px;
}

.card .card-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 12px;
  font-size: 0.8rem;
}

.tag {
  display: inline-block;
  padding: 3px 10px;
  background: #eef2ff;
  color: var(--color-primary);
  border-radius: 999px;
  font-size: 0.8rem;
}

.tag.tag-level-easy {
  background: #ecfdf5;
  color: #065f46;
}

.tag.tag-level-mid {
  background: #fff7ed;
  color: #9a3412;
}

.tag.tag-level-hard {
  background: #fef2f2;
  color: #991b1b;
}

/* ============ Hero ============ */
.hero {
  background: linear-gradient(135deg, #4f46e5 0%, #10b981 100%);
  color: #ffffff;
  padding: 48px 28px;
  border-radius: var(--radius-lg);
  text-align: center;
  margin-bottom: 28px;
}

.hero h1 {
  color: #ffffff;
  font-size: 2.2rem;
  margin-bottom: 12px;
}

.hero p {
  color: rgba(255, 255, 255, 0.9);
  max-width: 640px;
  margin: 0 auto 20px;
}

.hero .btn {
  background: #ffffff;
  color: var(--color-primary);
  border-color: #ffffff;
}

.hero .btn:hover {
  background: #eef2ff;
}

/* ============ 徽章/成就 ============ */
.badge-card {
  text-align: center;
  padding: 24px;
}

.badge-card .badge-icon {
  font-size: 2.5rem;
  margin-bottom: 10px;
}

.badge-card .badge-points {
  color: var(--color-accent);
  font-weight: 600;
  font-size: 0.9rem;
}

/* ============ Toast ============ */
.toast-container {
  position: fixed;
  top: calc(var(--nav-height) + 16px);
  right: 20px;
  display: flex;
  flex-direction: column;
  gap: 10px;
  z-index: 2000;
  pointer-events: none;
}

.toast {
  min-width: 220px;
  max-width: 320px;
  padding: 12px 16px;
  background: var(--color-info);
  color: #ffffff;
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-lg);
  font-size: 0.9rem;
  opacity: 0;
  transform: translateX(20px);
  transition: opacity 0.25s ease, transform 0.25s ease;
  pointer-events: auto;
}

.toast.show {
  opacity: 1;
  transform: translateX(0);
}

.toast.info {
  background: var(--color-info);
}

.toast.success {
  background: var(--color-success);
}

.toast.warning {
  background: var(--color-warning);
}

.toast.error {
  background: var(--color-error);
}

/* ============ 课程详情 ============ */
.course-detail {
  background: var(--color-bg-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 28px;
  box-shadow: var(--shadow-sm);
}

.course-detail .course-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 16px 0;
}

/* ============ 404 ============ */
.not-found {
  text-align: center;
  padding: 80px 20px;
}

.not-found .code {
  font-size: 5rem;
  font-weight: 800;
  color: var(--color-primary);
  margin: 0;
  line-height: 1;
}

/* ============ Footer ============ */
.site-footer {
  border-top: 1px solid var(--color-border);
  background: #ffffff;
  padding: 20px;
  text-align: center;
  color: var(--color-text-light);
  font-size: 0.85rem;
}

/* ============ 响应式 ============ */
.course-layout {
  display: grid;
  grid-template-columns: 260px 1fr;
  gap: 24px;
}

.toc {
  background: #ffffff;
  border-radius: 10px;
  padding: 16px;
  border: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
  align-self: start;
  position: sticky;
  top: calc(var(--nav-height) + 16px);
}

.toc h3 {
  margin-top: 0;
  font-size: 1rem;
  color: var(--color-text);
}

.toc ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

.toc li {
  margin-bottom: 6px;
}

.toc a {
  display: block;
  padding: 8px 10px;
  color: var(--color-text);
  text-decoration: none;
  border-radius: 8px;
  font-size: 0.92rem;
  transition: background-color 0.15s ease, color 0.15s ease;
}

.toc a:hover {
  background: #eef2ff;
  color: var(--color-primary);
}

.toc a.active {
  background: var(--color-primary);
  color: #ffffff;
}

.toc a.exam {
  margin-top: 12px;
  border-top: 1px dashed var(--color-border);
  padding-top: 12px;
  font-weight: 600;
}

.code-block {
  background: #0f172a;
  color: #e2e8f0;
  border-radius: 10px;
  padding: 16px;
  font-family: ui-monospace, Menlo, Consolas, monospace;
  font-size: 0.9rem;
  white-space: pre;
  overflow-x: auto;
  position: relative;
  margin: 12px 0;
}

.code-actions {
  position: absolute;
  top: 10px;
  right: 10px;
  display: flex;
  gap: 6px;
}

.code-actions button {
  background: #334155;
  color: #e2e8f0;
  border: none;
  border-radius: 6px;
  padding: 6px 10px;
  cursor: pointer;
  font-size: 0.8rem;
}

.code-actions button:hover {
  background: #475569;
}

.highlight-box {
  background: #fffbeb;
  border-left: 4px solid var(--color-accent);
  padding: 12px 14px;
  border-radius: 6px;
  margin: 12px 0;
  color: #78350f;
}

.quiz-block {
  background: #ffffff;
  border: 1px solid var(--color-border);
  border-radius: 10px;
  padding: 18px 20px;
  margin-bottom: 18px;
}

.quiz-block .q-title {
  font-weight: 600;
  margin-bottom: 10px;
  color: var(--color-text);
}

.quiz-block .q-option {
  padding: 8px 10px;
  border-radius: 8px;
  cursor: pointer;
  border: 1px solid var(--color-border);
  margin-bottom: 8px;
  user-select: none;
  transition: background-color 0.15s ease, border-color 0.15s ease;
}

.quiz-block .q-option:hover {
  background: #f8fafc;
}

.quiz-block .q-option.selected {
  background: #eef2ff;
  border-color: var(--color-primary);
}

.quiz-block .q-option.correct {
  background: #ecfdf5;
  border-color: var(--color-success);
}

.quiz-block .q-option.wrong {
  background: #fef2f2;
  border-color: var(--color-error);
}

.quiz-block input[type="text"],
.quiz-block textarea {
  width: 100%;
  padding: 8px 10px;
  border: 1px solid var(--color-border);
  border-radius: 8px;
  font-size: 0.92rem;
  font-family: inherit;
}

.quiz-block textarea {
  font-family: ui-monospace, Menlo, Consolas, monospace;
  min-height: 80px;
  resize: vertical;
}

.q-explain {
  font-size: 0.85rem;
  color: var(--color-text-light);
  margin-top: 10px;
  padding-top: 8px;
  border-top: 1px dashed var(--color-border);
}

.chapter-nav {
  display: flex;
  justify-content: space-between;
  margin: 24px 0;
  gap: 12px;
}

.chapter-nav .btn {
  flex: 1;
}

.progress-bar {
  height: 8px;
  background: #eef2ff;
  border-radius: 999px;
  overflow: hidden;
}

.progress-bar > span {
  display: block;
  height: 100%;
  background: var(--color-primary);
  transition: width 0.3s;
}

.course-meta-block {
  display: flex;
  align-items: center;
  gap: 14px;
  flex-wrap: wrap;
  margin: 12px 0;
}

.chapter-title {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.section-separator {
  height: 1px;
  background: var(--color-border);
  margin: 18px 0;
}

.exam-header {
  background: linear-gradient(135deg, #4f46e5 0%, #10b981 100%);
  color: #ffffff;
  padding: 18px 20px;
  border-radius: 10px;
  margin-bottom: 18px;
}

.exam-header h2 {
  color: #ffffff;
  margin: 0 0 6px;
}

.exam-summary {
  background: #ffffff;
  border: 1px solid var(--color-border);
  border-radius: 10px;
  padding: 18px;
  margin-top: 18px;
  text-align: center;
}

.exam-summary .score {
  font-size: 2.4rem;
  font-weight: 700;
  color: var(--color-primary);
  margin: 8px 0;
}

@media (max-width: 760px) {
  .course-layout {
    grid-template-columns: 1fr;
  }

  .toc {
    position: static;
  }

  .chapter-nav {
    flex-direction: column;
  }
}

.earned {
  border-color: var(--color-accent);
  box-shadow: 0 6px 14px -8px rgba(245, 158, 11, 0.6);
}

.earned .badge-icon {
  filter: drop-shadow(0 2px 2px rgba(0, 0, 0, 0.15));
}

.stat-card {
  padding: 22px 20px;
  background: #fff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
}

.stat-card h3 {
  font-size: 1rem;
  color: var(--color-text-light);
  margin: 0 0 8px;
}

.stat-card .stat-value {
  font-size: 1.8rem;
  font-weight: 700;
  color: var(--color-primary);
}

.mini-bar-chart {
  display: flex;
  align-items: flex-end;
  gap: 8px;
  height: 100px;
  margin-top: 12px;
}

.mini-bar-chart > div {
  flex: 1;
  background: #c7d2fe;
  border-radius: 6px 6px 0 0;
  position: relative;
}

.mini-bar-chart > div.active {
  background: var(--color-primary);
}

.mini-bar-chart > div span {
  position: absolute;
  top: -18px;
  left: 0;
  right: 0;
  text-align: center;
  font-size: 0.7rem;
  color: var(--color-text-light);
}

@media (max-width: 640px) {
  .site-nav .menu a {
    padding: 6px 10px;
    font-size: 0.85rem;
  }

  .hero {
    padding: 32px 16px;
  }

  .hero h1 {
    font-size: 1.6rem;
  }

  h1 {
    font-size: 1.6rem;
  }
}

.tag-filter { cursor: pointer; background:#eef2ff; color:var(--color-primary); border:none; }
.tag-filter.active { background:var(--color-primary); color:#fff; }
.tag-filter-row { display:flex; flex-wrap:wrap; gap:8px; margin-top:10px; }
.filter-summary { font-size: 0.85rem; color: var(--color-text-light); margin-top: 10px; }
.btn-ghost { background:#fff; border:1px solid var(--color-border); color: var(--color-text); padding: 6px 12px; border-radius: 8px; cursor: pointer; font-size: 0.85rem; }

.site-nav .menu a { min-height: 40px; }
input, button { font-size: 1rem; }

@media (max-width: 900px) {
  .course-layout { grid-template-columns: 1fr; }
  .toc { position: static; }
}

@media (max-width: 520px) {
  .hero { padding: 28px 14px; }
  .hero h1 { font-size: 1.5rem; }
  .card { padding: 16px; }
}

.code-block { font-size: 0.82rem; line-height: 1.5; }
.q-option input { margin-right: 8px; }
.chapter-nav .btn { min-width: 110px; }

a:focus-visible, button:focus-visible, input:focus-visible { outline: 2px solid var(--color-primary); outline-offset: 2px; }