/* ========== 1. 变量与基础 ========== */
:root {
  --color-primary: #0055FF;
  --color-deep: #003399;
  --color-accent: #FF6600;
  --color-paper: #FAF5EB;
  --color-white: #FFFFFF;
  --color-ink: #1A1A2E;
  --color-muted: #6E7B8A;
  --color-border: #D9E2EC;
  --color-success: #00C48C;
  --color-warning: #FFCC00;
  --font-heading: "Inter", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-body: "Roboto", "PingFang SC", "Microsoft YaHei", sans-serif;
  --container-width: 1200px;
  --container-narrow: 820px;
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-pill: 999px;
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 24px;
  --space-6: 32px;
  --space-7: 48px;
  --space-8: 64px;
  --transition-fast: 0.15s ease;
  --transition: 0.25s ease;
  --shadow-sm: 0 2px 8px rgba(26, 26, 46, 0.06);
  --shadow: 0 4px 16px rgba(26, 26, 46, 0.08);
  --shadow-lg: 0 10px 30px rgba(26, 26, 46, 0.1);
}

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.7;
  color: var(--color-ink);
  background: var(--color-paper);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  font-weight: 700;
  line-height: 1.2;
  color: var(--color-ink);
  margin: 0 0 var(--space-4);
}

h1 { font-size: 40px; letter-spacing: -0.02em; }
h2 { font-size: 32px; letter-spacing: -0.01em; }
h3 { font-size: 24px; }
h4 { font-size: 20px; }
h5 { font-size: 18px; }
h6 { font-size: 16px; }

p {
  margin: 0 0 var(--space-4);
}

ul, ol {
  list-style: none;
}

img {
  display: block;
  max-width: 100%;
  height: auto;
}

button, input, select, textarea {
  font: inherit;
}

button {
  background: none;
  border: none;
  padding: 0;
  cursor: pointer;
  color: inherit;
}

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

a:hover {
  color: var(--color-deep);
}

:focus-visible {
  outline: 3px solid var(--color-accent);
  outline-offset: 2px;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

main {
  display: block;
  flex: 1 0 auto;
}

/* ========== 2. 文本工具 ========== */
.text-muted { color: var(--color-muted); }
.text-small { font-size: 14px; }
.text-primary { color: var(--color-primary); }
.text-accent { color: var(--color-accent); }

/* ========== 3. 布局容器 ========== */
.site-container {
  max-width: var(--container-width);
  margin-inline: auto;
  padding-inline: var(--space-5);
  width: 100%;
}

.site-container--narrow {
  max-width: var(--container-narrow);
}

.site-container--wide {
  max-width: 1440px;
}

.section {
  padding-block: var(--space-7);
}

.section--tight {
  padding-block: var(--space-5);
}

.section--alt {
  background: rgba(0, 85, 255, 0.05);
}

/* ========== 4. 可访问性与进度 ========== */
.skip-link {
  position: fixed;
  top: -100%;
  left: 16px;
  z-index: 2000;
  background: var(--color-ink);
  color: #fff;
  padding: 12px 24px;
  border-radius: 0 0 var(--radius-sm) var(--radius-sm);
  font-family: var(--font-heading);
  font-size: 14px;
  font-weight: 700;
  text-decoration: none;
  transition: top var(--transition);
}

.skip-link:focus-visible {
  top: 0;
}

.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 1000;
  width: 100%;
  height: 3px;
  pointer-events: none;
  background: rgba(26, 26, 46, 0.08);
}

.scroll-progress-bar {
  display: block;
  width: 0%;
  height: 100%;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent));
  border-radius: 0 3px 3px 0;
  transition: width 0.1s linear;
}

/* ========== 5. 页头与导航 ========== */
.site-header {
  position: relative;
  background: var(--color-paper);
  border-top: 4px solid var(--color-primary);
  flex-shrink: 0;
}

.masthead {
  background: var(--color-paper);
}

.masthead-inner {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-5);
  padding-block: 22px;
}

.brand-lockup {
  display: inline-flex;
  align-items: center;
  gap: 14px;
  color: var(--color-ink);
  text-decoration: none;
}

.brand-lockup:hover {
  color: var(--color-ink);
}

.brand-mark {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 54px;
  height: 54px;
  background: var(--color-primary);
  color: #fff;
  font-family: var(--font-heading);
  font-size: 17px;
  font-weight: 900;
  letter-spacing: 0.04em;
  border-radius: 14px;
  box-shadow: 4px 4px 0 rgba(255, 102, 0, 0.45);
  flex-shrink: 0;
}

.brand-mark-dot {
  position: absolute;
  right: -4px;
  bottom: -4px;
  width: 14px;
  height: 14px;
  background: var(--color-accent);
  border-radius: 50%;
  border: 2px solid var(--color-paper);
}

.brand-copy {
  display: flex;
  flex-direction: column;
  gap: 0;
}

.brand-name {
  font-family: var(--font-heading);
  font-size: 22px;
  font-weight: 900;
  color: var(--color-ink);
  line-height: 1.1;
  letter-spacing: 0.02em;
}

.brand-tagline {
  font-size: 13px;
  color: var(--color-muted);
  letter-spacing: 0.08em;
  line-height: 1.4;
  margin-top: 3px;
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: 8px;
  padding: 10px 16px;
  background: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-family: var(--font-heading);
  font-size: 14px;
  font-weight: 700;
  color: var(--color-ink);
  cursor: pointer;
  transition: border-color var(--transition-fast), color var(--transition-fast), box-shadow var(--transition-fast);
}

.nav-toggle:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}

.nav-toggle-box {
  display: inline-flex;
  flex-direction: column;
  gap: 4px;
  width: 18px;
}

.nav-toggle-bar {
  display: block;
  height: 2px;
  background: currentColor;
  border-radius: 2px;
  transition: transform var(--transition), opacity var(--transition);
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(2) {
  opacity: 0;
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

.nav-toggle-text {
  font-weight: 700;
  font-size: 14px;
}

.site-nav {
  background: var(--color-white);
  border-top: 1px solid var(--color-border);
  border-bottom: 1px solid var(--color-border);
}

.site-nav-list {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 2px;
}

.site-nav-link {
  display: inline-block;
  padding: 14px 18px;
  font-family: var(--font-heading);
  font-size: 15px;
  font-weight: 700;
  color: var(--color-ink);
  text-decoration: none;
  position: relative;
  border-radius: var(--radius-sm) var(--radius-sm) 0 0;
  transition: color var(--transition-fast), background var(--transition-fast);
}

.site-nav-link:hover {
  color: var(--color-primary);
  background: rgba(0, 85, 255, 0.06);
  text-decoration: none;
}

.site-nav-link[aria-current="page"] {
  color: var(--color-primary);
  background: rgba(0, 85, 255, 0.08);
}

.site-nav-link[aria-current="page"]::after {
  content: "";
  position: absolute;
  bottom: -1px;
  left: 14px;
  right: 14px;
  height: 3px;
  background: var(--color-accent);
  border-radius: 3px 3px 0 0;
}

/* ========== 6. 页脚 ========== */
.site-footer {
  background: var(--color-deep);
  color: rgba(255, 255, 255, 0.85);
  flex-shrink: 0;
  margin-top: var(--space-8);
}

.site-footer a {
  color: rgba(255, 255, 255, 0.85);
  text-decoration: none;
  transition: color var(--transition-fast);
}

.site-footer a:hover {
  color: var(--color-accent);
}

.site-footer-grid {
  display: grid;
  grid-template-columns: 2.2fr 1.2fr 1.2fr 1.8fr;
  gap: 40px;
  padding-block: 48px 40px;
}

.footer-brand-name {
  font-family: var(--font-heading);
  font-size: 24px;
  font-weight: 900;
  color: #fff;
  line-height: 1.2;
  margin-bottom: 0;
}

.footer-brand-tagline {
  font-size: 14px;
  color: rgba(255, 255, 255, 0.7);
  letter-spacing: 0.08em;
  margin-top: 4px;
  margin-bottom: 0;
}

.footer-trust {
  margin-top: 18px;
  margin-bottom: 0;
  font-size: 14px;
  line-height: 1.8;
  color: rgba(255, 255, 255, 0.78);
  border-left: 3px solid var(--color-accent);
  padding-left: 12px;
}

.footer-note {
  margin-top: 20px;
  margin-bottom: 0;
  font-size: 13px;
  line-height: 1.6;
  color: rgba(255, 255, 255, 0.65);
  background: rgba(255, 255, 255, 0.06);
  border-radius: var(--radius-sm);
  padding: 12px 16px;
}

.footer-col {
  min-width: 0;
}

.footer-heading {
  font-family: var(--font-heading);
  font-size: 15px;
  font-weight: 800;
  color: #fff;
  margin-bottom: 16px;
  letter-spacing: 0.04em;
}

.footer-heading::before {
  content: "";
  display: inline-block;
  width: 5px;
  height: 16px;
  background: var(--color-accent);
  border-radius: 3px;
  margin-right: 8px;
  vertical-align: -2px;
}

.footer-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.footer-list a {
  display: inline-block;
  padding-block: 2px;
}

.footer-contact-list li {
  display: flex;
  gap: 8px;
  align-items: flex-start;
  font-size: 14px;
  line-height: 1.7;
}

.footer-contact-label {
  display: inline-block;
  flex: 0 0 32px;
  font-weight: 700;
  color: #fff;
}

.site-footer-bottom {
  border-top: 1px solid rgba(255, 255, 255, 0.12);
  background: rgba(0, 0, 0, 0.18);
  padding-block: 14px;
}

.site-footer-bottom-inner {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 6px 24px;
  font-size: 13px;
  color: rgba(255, 255, 255, 0.65);
}

.site-footer-bottom-inner p {
  margin: 0;
}

/* ========== 7. 按钮 ========== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 11px 24px;
  border: 2px solid transparent;
  border-radius: var(--radius-sm);
  font-family: var(--font-heading);
  font-size: 15px;
  font-weight: 700;
  line-height: 1.2;
  cursor: pointer;
  text-decoration: none;
  transition: background var(--transition-fast), border-color var(--transition-fast), transform var(--transition-fast), color var(--transition-fast), box-shadow var(--transition-fast);
}

.btn:hover {
  text-decoration: none;
  transform: translateY(-2px);
  box-shadow: var(--shadow-sm);
}

.btn--primary {
  background: var(--color-primary);
  color: #fff;
}

.btn--primary:hover {
  background: var(--color-deep);
  color: #fff;
  box-shadow: var(--shadow);
}

.btn--accent {
  background: var(--color-accent);
  color: #fff;
}

.btn--accent:hover {
  background: #E55C00;
  color: #fff;
  box-shadow: var(--shadow);
}

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

.btn--ghost:hover {
  background: rgba(0, 85, 255, 0.08);
  color: var(--color-deep);
}

.btn--sm {
  padding: 7px 14px;
  font-size: 14px;
}

/* ========== 8. 面包屑 ========== */
.breadcrumb {
  padding-block: 14px;
}

.breadcrumb-list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
  font-size: 14px;
}

.breadcrumb-item {
  display: flex;
  align-items: center;
  gap: 6px;
}

.breadcrumb-item + .breadcrumb-item::before {
  content: "/";
  color: var(--color-muted);
}

.breadcrumb-link {
  color: var(--color-muted);
  text-decoration: none;
  transition: color var(--transition-fast);
}

.breadcrumb-link:hover {
  color: var(--color-primary);
}

.breadcrumb-item--active {
  color: var(--color-ink);
  font-weight: 600;
}

/* ========== 9. 卡片 ========== */
.card {
  background: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-5);
  transition: box-shadow var(--transition), transform var(--transition);
}

.card:hover {
  box-shadow: var(--shadow);
  transform: translateY(-4px);
}

.card--flat {
  background: transparent;
  border: none;
  border-radius: 0;
  padding: 0;
}

.card--primary {
  border-top: 4px solid var(--color-primary);
}

.card--accent {
  border-top: 4px solid var(--color-accent);
}

.card-title {
  font-family: var(--font-heading);
  font-size: 20px;
  font-weight: 700;
  color: var(--color-ink);
  margin-bottom: 8px;
}

.card-desc {
  font-size: 15px;
  color: var(--color-muted);
  line-height: 1.7;
  margin: 0;
}

.card-link {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-family: var(--font-heading);
  font-weight: 600;
  font-size: 15px;
  color: var(--color-primary);
  text-decoration: none;
  margin-top: 14px;
}

.card-link:hover {
  color: var(--color-deep);
}

.card-link::after {
  content: "→";
  transition: transform var(--transition-fast);
}

.card-link:hover::after {
  transform: translateX(4px);
}

/* ========== 10. 标签 ========== */
.tag {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 4px 12px;
  border-radius: var(--radius-pill);
  background: var(--color-paper);
  border: 1px solid var(--color-border);
  font-size: 13px;
  font-weight: 600;
  color: var(--color-ink);
  white-space: nowrap;
}

.tag--primary {
  background: rgba(0, 85, 255, 0.1);
  border-color: rgba(0, 85, 255, 0.2);
  color: var(--color-primary);
}

.tag--accent {
  background: rgba(255, 102, 0, 0.12);
  border-color: rgba(255, 102, 0, 0.25);
  color: #E55C00;
}

.tag--success {
  background: rgba(0, 196, 140, 0.12);
  border-color: rgba(0, 196, 140, 0.25);
  color: #008A61;
}

.tag--warning {
  background: rgba(255, 204, 0, 0.15);
  border-color: rgba(255, 204, 0, 0.35);
  color: #8A6D00;
}

.tag--dark {
  background: var(--color-ink);
  border-color: var(--color-ink);
  color: #fff;
}

/* ========== 11. 网格 ========== */
.grid {
  display: grid;
  gap: var(--space-5);
}

.grid--2 {
  grid-template-columns: repeat(2, 1fr);
}

.grid--3 {
  grid-template-columns: repeat(3, 1fr);
}

.grid--4 {
  grid-template-columns: repeat(4, 1fr);
}

.grid--split {
  grid-template-columns: 2fr 1fr;
}

.grid--split-flip {
  grid-template-columns: 1fr 2fr;
}

.grid--align-center {
  align-items: center;
}

/* ========== 12. 表格 ========== */
.table-wrap {
  overflow-x: auto;
  background: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
}

.table {
  width: 100%;
  border-collapse: collapse;
  font-size: 15px;
}

.table th,
.table td {
  padding: 12px 16px;
  border-bottom: 1px solid var(--color-border);
  text-align: left;
  vertical-align: top;
}

.table th {
  font-family: var(--font-heading);
  font-weight: 700;
  font-size: 14px;
  color: var(--color-ink);
  background: var(--color-paper);
  white-space: nowrap;
}

.table tr:last-child th,
.table tr:last-child td {
  border-bottom: none;
}

.table tbody tr:hover td {
  background: rgba(0, 85, 255, 0.03);
}

/* ========== 13. 提示块 ========== */
.callout {
  padding: 16px 20px;
  background: var(--color-white);
  border: 1px solid var(--color-border);
  border-left: 4px solid var(--color-primary);
  border-radius: var(--radius-sm);
  font-size: 15px;
}

.callout--accent {
  border-left-color: var(--color-accent);
}

.callout--success {
  border-left-color: var(--color-success);
}

.callout--warning {
  border-left-color: var(--color-warning);
  background: rgba(255, 204, 0, 0.08);
}

/* ========== 14. 视觉占位与章节眉题 ========== */
.section-label {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-family: var(--font-heading);
  font-size: 14px;
  font-weight: 800;
  letter-spacing: 0.1em;
  color: var(--color-primary);
  margin-bottom: 12px;
}

.section-label::before {
  content: "";
  width: 24px;
  height: 3px;
  background: var(--color-accent);
  border-radius: 3px;
}

.visual {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 180px;
  background: linear-gradient(135deg, #E8F0FE, #D9E2EC);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.visual--blue {
  background: linear-gradient(135deg, var(--color-primary), var(--color-deep));
}

.visual--paper {
  background: var(--color-paper);
  border: 1px dashed var(--color-border);
}

.visual--ratio {
  aspect-ratio: 16 / 9;
}

.visual--ratio-square {
  aspect-ratio: 1 / 1;
}

.visual--ratio-portrait {
  aspect-ratio: 4 / 5;
}

.visual-label {
  position: relative;
  z-index: 1;
  font-family: var(--font-heading);
  font-size: 14px;
  font-weight: 700;
  color: var(--color-primary);
  background: var(--color-white);
  padding: 8px 18px;
  border-radius: var(--radius-pill);
  box-shadow: var(--shadow-sm);
}

.visual--blue .visual-label {
  color: #fff;
  background: rgba(255, 255, 255, 0.2);
}

/* ========== 15. 标签页 ========== */
.tabs {
  background: var(--color-white);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.tabs-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0;
  background: var(--color-paper);
  border-bottom: 1px solid var(--color-border);
}

.tabs-trigger {
  padding: 12px 20px;
  font-family: var(--font-heading);
  font-size: 15px;
  font-weight: 700;
  color: var(--color-muted);
  cursor: pointer;
  border-bottom: 3px solid transparent;
  margin-bottom: -1px;
  transition: color var(--transition-fast), border-color var(--transition-fast), background var(--transition-fast);
}

.tabs-trigger:hover {
  color: var(--color-primary);
}

.tabs-trigger[aria-selected="true"] {
  color: var(--color-primary);
  border-bottom-color: var(--color-accent);
  background: var(--color-white);
}

.tabs-panel {
  padding: var(--space-5);
}

/* ========== 16. 响应式 ========== */
@media (max-width: 1023px) {
  .grid--4 {
    grid-template-columns: repeat(2, 1fr);
  }

  .grid--split,
  .grid--split-flip {
    grid-template-columns: 1fr;
  }

  .site-footer-grid {
    grid-template-columns: 1fr 1fr;
    gap: 32px;
  }
}

@media (max-width: 819px) {
  .nav-toggle {
    display: inline-flex;
  }

  .masthead-inner {
    justify-content: space-between;
  }

  .site-nav {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    z-index: 100;
    background: var(--color-white);
    border-top: none;
    border-bottom: 1px solid var(--color-border);
    box-shadow: var(--shadow-lg);
    visibility: hidden;
    opacity: 0;
    transform: translateY(-10px);
    transition: opacity var(--transition), transform var(--transition), visibility var(--transition);
  }

  .site-nav[data-open] {
    visibility: visible;
    opacity: 1;
    transform: translateY(0);
  }

  .site-nav-list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding-block: 8px;
  }

  .site-nav-link {
    display: block;
    width: 100%;
    padding: 14px 24px;
    border-radius: 0;
  }

  .site-nav-link[aria-current="page"] {
    border-inline-start: 4px solid var(--color-primary);
    border-radius: 0;
    background: rgba(0, 85, 255, 0.08);
  }

  .site-nav-link[aria-current="page"]::after {
    display: none;
  }
}

@media (max-width: 767px) {
  .grid--2,
  .grid--3,
  .grid--4 {
    grid-template-columns: 1fr;
  }

  .grid--split,
  .grid--split-flip {
    grid-template-columns: 1fr;
  }

  h1 { font-size: 32px; }
  h2 { font-size: 28px; }
  h3 { font-size: 22px; }

  .masthead-inner {
    padding-block: 16px;
  }

  .section {
    padding-block: var(--space-6);
  }
}

@media (max-width: 639px) {
  .site-footer-grid {
    grid-template-columns: 1fr;
    gap: 28px;
  }

  .site-footer-bottom-inner {
    flex-direction: column;
    align-items: flex-start;
  }
}

/* ========== 17. 动效降级 ========== */
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}