/* ===== 基盘变量 ===== */
:root {
  --c-purple: #B026FF;
  --c-blue: #00F0FF;
  --c-orange: #FF6B00;
  --c-black: #0A0A12;
  --c-card: #10101F;
  --c-white: #F5F7FF;
  --c-gray: #A0A0B8;
  --c-green: #00E676;
  --c-red: #FF3D3D;
  --c-line: rgba(255, 255, 255, 0.1);
  --c-purple-soft: rgba(176, 38, 255, 0.12);
  --c-blue-soft: rgba(0, 240, 255, 0.08);
  --c-orange-soft: rgba(255, 107, 0, 0.15);

  --font-head: "Archivo Black", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-body: "Inter", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-mono: "JetBrains Mono", "SF Mono", Consolas, monospace;

  --container: 1280px;
  --container-narrow: 760px;
  --space-sm: 1rem;
  --space-md: 2rem;
  --space-lg: 3rem;
  --space-xl: 5rem;
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --dur: 0.3s;
  --z-header: 100;
  --z-fixed: 101;
  --z-skip: 102;
  --z-progress: 103;
}

/* ===== 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-body);
  font-size: 1rem;
  line-height: 1.7;
  color: var(--c-white);
  background-color: var(--c-black);
  background-image:
    linear-gradient(rgba(255, 255, 255, 0.02) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.02) 1px, transparent 1px);
  background-size: 64px 64px;
  overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-head);
  font-weight: 900;
  line-height: 1.25;
  color: var(--c-white);
}

p {
  margin-bottom: 1rem;
}

a {
  color: var(--c-blue);
  text-decoration: none;
  transition:
    color var(--dur) var(--ease),
    border-color var(--dur) var(--ease),
    background var(--dur) var(--ease),
    box-shadow var(--dur) var(--ease),
    filter var(--dur) var(--ease);
}

a:hover {
  text-decoration: underline;
}

ul, ol {
  list-style: none;
}

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

button {
  font-family: inherit;
}

strong, b {
  font-weight: 700;
}

small {
  font-size: 0.875em;
}

/* ===== 基础工具 ===== */
.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;
}

.text-purple { color: var(--c-purple); }
.text-blue { color: var(--c-blue); }
.text-orange { color: var(--c-orange); }
.text-gray { color: var(--c-gray); }
.text-green { color: var(--c-green); }
.text-red { color: var(--c-red); }
.text-sm { font-size: 0.875rem; }
.text-xs { font-size: 0.75rem; }
.text-mono { font-family: var(--font-mono); }

.container {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: 1.5rem;
}

#main-content {
  outline: none;
}

/* ===== 焦点与动态偏好 ===== */
:focus-visible {
  outline: 2px solid var(--c-blue);
  outline-offset: 3px;
}

@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;
  }
}

/* ===== 跳转链接 ===== */
.skip-link {
  position: fixed;
  top: 0.5rem;
  left: 0.5rem;
  transform: translateY(-300%);
  z-index: var(--z-skip);
  background: var(--c-purple);
  color: var(--c-white);
  font-weight: 700;
  font-size: 0.875rem;
  padding: 0.75rem 1.25rem;
  box-shadow: 0 4px 20px rgba(176, 38, 255, 0.5);
  transition: transform 0.2s var(--ease);
}

.skip-link:focus {
  transform: translateY(0);
  color: var(--c-white);
  text-decoration: none;
}

/* ===== 滚动进度条 ===== */
.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  height: 3px;
  width: 0%;
  background: linear-gradient(90deg, var(--c-purple), var(--c-blue));
  z-index: var(--z-progress);
  pointer-events: none;
  box-shadow: 0 0 12px rgba(176, 38, 255, 0.5);
}

/* ===== 通用按钮 ===== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.75rem 1.625rem;
  font-family: var(--font-body);
  font-size: 0.875rem;
  font-weight: 700;
  line-height: 1;
  text-decoration: none;
  border: 1px solid transparent;
  border-radius: 0;
  cursor: pointer;
  white-space: nowrap;
  clip-path: polygon(0 0, 100% 0, calc(100% - 12px) 100%, 0 100%);
  transition:
    background var(--dur) var(--ease),
    color var(--dur) var(--ease),
    border-color var(--dur) var(--ease),
    transform var(--dur) var(--ease),
    filter var(--dur) var(--ease);
}

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

.btn:focus-visible {
  clip-path: none;
  outline: 2px solid var(--c-blue);
  outline-offset: 3px;
}

.btn--primary {
  background: var(--c-orange);
  color: var(--c-black);
}

.btn--primary:hover {
  background: #ff8533;
  filter: drop-shadow(0 0 14px rgba(255, 107, 0, 0.45));
}

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

.btn--ghost:hover {
  background: var(--c-blue-soft);
  border-color: var(--c-blue);
  filter: drop-shadow(0 0 12px rgba(0, 240, 255, 0.25));
}

.btn--purple {
  background: var(--c-purple);
  color: var(--c-white);
}

.btn--purple:hover {
  background: #c44dff;
  filter: drop-shadow(0 0 14px rgba(176, 38, 255, 0.45));
}

/* ===== 面包屑 ===== */
.breadcrumb {
  padding: 1.125rem 0;
  border-bottom: 1px solid var(--c-line);
  margin-bottom: var(--space-md);
}

.breadcrumb__list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.375rem;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--c-gray);
}

.breadcrumb__item {
  display: inline-flex;
  align-items: center;
}

.breadcrumb__item + .breadcrumb__item::before {
  content: "//";
  color: var(--c-gray);
  opacity: 0.4;
  margin-right: 0.375rem;
}

.breadcrumb__link {
  color: var(--c-gray);
  transition: color var(--dur) var(--ease);
}

.breadcrumb__link:hover {
  color: var(--c-blue);
  text-decoration: none;
}

.breadcrumb__item--current {
  color: var(--c-purple);
}

/* ===== 内容区域 ===== */
.content-area {
  padding: var(--space-md) 0 6rem;
}

.content-area--narrow {
  max-width: var(--container-narrow);
  margin-inline: auto;
}

/* ===== 章节 ===== */
.section {
  padding: var(--space-lg) 0;
  position: relative;
}

.section__head {
  display: flex;
  gap: var(--space-md);
  align-items: flex-start;
  margin-bottom: var(--space-md);
}

.section__side {
  flex: 0 0 160px;
  max-width: 200px;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  line-height: 1.7;
  color: var(--c-gray);
  border-left: 2px solid var(--c-purple);
  padding-left: 1rem;
  margin-top: 0.5rem;
}

.section__main {
  flex: 1;
  min-width: 0;
}

.section__title {
  font-size: clamp(1.5rem, 3vw, 2.25rem);
  margin-bottom: 0.5rem;
}

.section__title::before {
  content: "";
  display: inline-block;
  width: 10px;
  height: 10px;
  margin-right: 0.75rem;
  background: var(--c-purple);
  box-shadow: 0 0 12px rgba(176, 38, 255, 0.8);
  vertical-align: 0.2em;
}

.section__subtitle {
  color: var(--c-gray);
  font-size: 0.95rem;
  line-height: 1.8;
  margin-bottom: 0;
}

.section-label {
  display: inline-flex;
  align-items: center;
  gap: 0.625rem;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--c-purple);
  margin-bottom: 1rem;
}

.section-label::before {
  content: "";
  width: 28px;
  height: 2px;
  background: var(--c-purple);
}

/* ===== 栅格 ===== */
.grid {
  display: grid;
  gap: 1.5rem;
}

.grid--2 { grid-template-columns: repeat(2, 1fr); }
.grid--3 { grid-template-columns: repeat(3, 1fr); }
.grid--4 { grid-template-columns: repeat(4, 1fr); }

/* ===== 卡片 ===== */
.card {
  background: var(--c-card);
  border: 1px solid var(--c-line);
  padding: 1.5rem;
  position: relative;
  transition:
    border-color var(--dur) var(--ease),
    transform var(--dur) var(--ease),
    box-shadow var(--dur) var(--ease);
}

.card:hover {
  border-color: rgba(176, 38, 255, 0.4);
  transform: translateY(-4px);
  box-shadow: 0 8px 32px rgba(176, 38, 255, 0.12);
}

.card--glow::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 3px;
  height: 100%;
  background: linear-gradient(var(--c-purple), var(--c-blue));
}

.card__title {
  font-family: var(--font-head);
  font-size: 1.125rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.card__text {
  color: var(--c-gray);
  font-size: 0.9rem;
  margin-bottom: 0;
}

/* ===== 标签 ===== */
.tag {
  display: inline-flex;
  align-items: center;
  padding: 0.25rem 0.75rem;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--c-gray);
  background: var(--c-card);
  border: 1px solid var(--c-line);
  border-radius: 0;
  line-height: 1.6;
}

.tag--purple {
  color: var(--c-purple);
  border-color: rgba(176, 38, 255, 0.4);
  background: rgba(176, 38, 255, 0.08);
}

.tag--blue {
  color: var(--c-blue);
  border-color: rgba(0, 240, 255, 0.4);
  background: rgba(0, 240, 255, 0.08);
}

.tag--orange {
  color: var(--c-orange);
  border-color: rgba(255, 107, 0, 0.4);
  background: rgba(255, 107, 0, 0.08);
}

/* ===== 数据面板 ===== */
.data-panel {
  background: var(--c-card);
  border: 1px solid var(--c-line);
  padding: 1.25rem;
  font-family: var(--font-mono);
  position: relative;
}

.data-panel__label {
  display: block;
  font-size: 0.7rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--c-gray);
  margin-bottom: 0.375rem;
}

.data-panel__value {
  display: block;
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--c-blue);
  line-height: 1.2;
}

.data-panel__value--purple { color: var(--c-purple); }
.data-panel__value--orange { color: var(--c-orange); }
.data-panel__value--green { color: var(--c-green); }

/* ===== 媒体占位框架 ===== */
.media-frame {
  position: relative;
  background: var(--c-card);
  border: 1px solid var(--c-line);
  overflow: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  aspect-ratio: 16 / 9;
  min-height: 180px;
}

.media-frame::before {
  content: attr(data-label);
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.3em;
  text-transform: uppercase;
  color: var(--c-gray);
  border: 1px solid var(--c-line);
  padding: 0.375rem 1rem;
  z-index: 1;
}

.media-frame::after {
  content: "";
  position: absolute;
  inset: 0;
  background:
    linear-gradient(135deg, rgba(176, 38, 255, 0.08), transparent 50%, rgba(0, 240, 255, 0.08));
  pointer-events: none;
}

.media-frame--16x9 { aspect-ratio: 16 / 9; }
.media-frame--4x3 { aspect-ratio: 4 / 3; }
.media-frame--square { aspect-ratio: 1 / 1; }

/* ===== 注释与分隔线 ===== */
.note {
  font-size: 0.875rem;
  color: var(--c-gray);
  border-left: 3px solid var(--c-blue);
  background: rgba(0, 240, 255, 0.04);
  padding: 1rem 1.25rem;
  margin: 1.5rem 0;
}

.note--warn {
  border-left-color: var(--c-orange);
  background: rgba(255, 107, 0, 0.06);
}

.note--error {
  border-left-color: var(--c-red);
  background: rgba(255, 61, 61, 0.06);
}

.divider {
  height: 1px;
  border: 0;
  background: linear-gradient(90deg, transparent, var(--c-line), transparent);
  margin: var(--space-lg) 0;
}

.divider--glow {
  background: linear-gradient(90deg, transparent, var(--c-purple), transparent);
  height: 1px;
}

/* ===== 页头 ===== */
.site-header {
  position: relative;
  background: var(--c-black);
  border-bottom: 1px solid var(--c-line);
  z-index: var(--z-header);
}

.site-header__topbar {
  background: var(--c-card);
  border-bottom: 1px solid var(--c-line);
  padding: 0.4rem 0;
}

.site-header__topbar-inner {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: var(--space-sm);
}

.site-header__trust {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--c-gray);
  letter-spacing: 0.03em;
  margin: 0;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
}

.site-header__trust::before {
  content: "";
  width: 6px;
  height: 6px;
  background: var(--c-green);
  box-shadow: 0 0 8px var(--c-green);
  flex-shrink: 0;
}

.site-header__masthead {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  padding: 2rem 0;
  position: relative;
  background: radial-gradient(ellipse at 50% 50%, rgba(176, 38, 255, 0.08), transparent 70%);
}

.site-header__brand {
  grid-column: 2;
  justify-self: center;
  display: flex;
  align-items: center;
  gap: 1rem;
  color: var(--c-white);
  text-decoration: none;
}

.site-header__brand:hover {
  text-decoration: none;
}

.site-header__brand-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 3rem;
  height: 3rem;
  padding: 0 0.5rem;
  background: linear-gradient(135deg, var(--c-purple), var(--c-blue));
  color: var(--c-black);
  font-family: var(--font-head);
  font-weight: 900;
  font-size: 1.1rem;
  letter-spacing: -0.02em;
  clip-path: polygon(8px 0, 100% 0, calc(100% - 8px) 100%, 0 100%);
  filter: drop-shadow(0 0 10px rgba(176, 38, 255, 0.4));
  transition: filter var(--dur) var(--ease);
}

.site-header__brand:hover .site-header__brand-mark {
  filter: drop-shadow(0 0 16px rgba(176, 38, 255, 0.7));
}

.site-header__brand-text {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
}

.site-header__logo {
  font-family: var(--font-head);
  font-size: 1.625rem;
  font-weight: 900;
  line-height: 1.15;
  letter-spacing: 0.03em;
  color: var(--c-white);
}

.site-header__logo-accent {
  color: var(--c-purple);
  margin: 0 0.25em;
}

.site-header__tagline {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--c-gray);
  margin-top: 0.25rem;
}

.site-header__actions {
  grid-column: 3;
  justify-self: end;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.site-header__action {
  padding: 0.625rem 1.375rem;
  font-size: 0.813rem;
}

.site-header__nav {
  background: var(--c-card);
  border-top: 1px solid var(--c-line);
  border-bottom: 1px solid var(--c-line);
}

.site-header__nav-list {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 0.25rem;
}

.site-header__nav-link {
  display: block;
  position: relative;
  padding: 0.75rem 1.25rem;
  font-family: var(--font-head);
  font-size: 0.875rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  color: var(--c-white);
  text-decoration: none;
  transition:
    color var(--dur) var(--ease),
    background var(--dur) var(--ease),
    text-shadow var(--dur) var(--ease);
}

.site-header__nav-link::after {
  content: "";
  position: absolute;
  left: 1.25rem;
  right: 1.25rem;
  bottom: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--c-purple), var(--c-blue));
  transform: scaleX(0);
  transform-origin: left;
  opacity: 0;
  transition: transform 0.35s var(--ease), opacity 0.35s var(--ease);
}

.site-header__nav-link:hover {
  color: var(--c-blue);
  background: rgba(0, 240, 255, 0.04);
  text-decoration: none;
  text-shadow: 0 0 16px rgba(0, 240, 255, 0.5);
}

.site-header__nav-link:hover::after,
.site-header__nav-link:focus-visible::after {
  transform: scaleX(1);
  opacity: 1;
}

.site-header__nav-link[aria-current="page"] {
  color: var(--c-purple);
  background: var(--c-purple-soft);
  text-shadow: 0 0 16px rgba(176, 38, 255, 0.4);
}

.site-header__nav-link[aria-current="page"]::after {
  transform: scaleX(1);
  opacity: 1;
  background: var(--c-orange);
}

.site-header__nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  width: 44px;
  height: 44px;
  background: transparent;
  border: 1px solid var(--c-line);
  padding: 0;
  cursor: pointer;
  border-radius: 0;
  transition:
    border-color var(--dur) var(--ease),
    background var(--dur) var(--ease);
}

.site-header__nav-toggle:hover {
  border-color: var(--c-purple);
  background: var(--c-purple-soft);
}

.site-header__nav-toggle-icon,
.site-header__nav-toggle-icon::before,
.site-header__nav-toggle-icon::after {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--c-white);
  transition:
    transform 0.3s var(--ease),
    background 0.3s var(--ease);
}

.site-header__nav-toggle-icon {
  position: relative;
}

.site-header__nav-toggle-icon::before,
.site-header__nav-toggle-icon::after {
  content: "";
  position: absolute;
  left: 0;
  top: 0;
}

.site-header__nav-toggle-icon::before {
  transform: translateY(-7px);
}

.site-header__nav-toggle-icon::after {
  transform: translateY(7px);
}

.site-header__nav-toggle[aria-expanded="true"] .site-header__nav-toggle-icon {
  background: transparent;
}

.site-header__nav-toggle[aria-expanded="true"] .site-header__nav-toggle-icon::before {
  transform: translateY(0) rotate(45deg);
}

.site-header__nav-toggle[aria-expanded="true"] .site-header__nav-toggle-icon::after {
  transform: translateY(0) rotate(-45deg);
}

/* ===== 页脚 ===== */
.site-footer {
  position: relative;
  margin-top: var(--space-xl);
  background: var(--c-black);
  border-top: 1px solid var(--c-line);
  overflow: hidden;
}

.site-footer::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--c-purple), var(--c-blue), var(--c-orange));
  z-index: 1;
}

.site-footer::after {
  content: "";
  position: absolute;
  top: -150px;
  right: -100px;
  width: 350px;
  height: 350px;
  background: radial-gradient(circle, rgba(176, 38, 255, 0.12), transparent 70%);
  pointer-events: none;
}

.site-footer__grid {
  display: grid;
  grid-template-columns: 1.6fr 1fr 1fr 1.4fr;
  gap: var(--space-md);
  padding: var(--space-lg) 0;
  position: relative;
}

.site-footer__col {
  min-width: 0;
}

.site-footer__col--brand {
  position: relative;
}

.site-footer__col--brand::before {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  width: 48px;
  height: 2px;
  background: var(--c-orange);
}

.site-footer__brand {
  display: inline-flex;
  flex-direction: column;
  align-items: flex-start;
  color: var(--c-white);
  text-decoration: none;
}

.site-footer__brand:hover {
  text-decoration: none;
}

.site-footer__logo {
  font-family: var(--font-head);
  font-size: 1.5rem;
  font-weight: 900;
  line-height: 1.2;
  color: var(--c-white);
  letter-spacing: 0.03em;
}

.site-footer__logo-accent {
  color: var(--c-purple);
}

.site-footer__tagline {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  color: var(--c-gray);
  margin-top: 0.375rem;
}

.site-footer__trust {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  line-height: 1.8;
  color: var(--c-gray);
  background: var(--c-card);
  border-left: 3px solid var(--c-purple);
  padding: 0.875rem 1rem;
  margin: 1.25rem 0 1.5rem;
  max-width: 340px;
}

.site-footer__heading {
  font-family: var(--font-head);
  font-size: 0.875rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--c-white);
  padding-bottom: 0.625rem;
  margin-bottom: 1.125rem;
  border-bottom: 1px solid var(--c-line);
  position: relative;
}

.site-footer__heading::after {
  content: "";
  position: absolute;
  bottom: -1px;
  left: 0;
  width: 32px;
  height: 2px;
  background: var(--c-purple);
}

.site-footer__links li {
  margin-bottom: 0.625rem;
}

.site-footer__links a {
  color: var(--c-gray);
  font-size: 0.875rem;
  transition:
    color var(--dur) var(--ease),
    padding-left var(--dur) var(--ease);
}

.site-footer__links a:hover {
  color: var(--c-blue);
  padding-left: 4px;
  text-decoration: none;
}

.site-footer__links--inline {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem 1rem;
}

.site-footer__links--inline li {
  margin-bottom: 0;
}

.site-footer__contact li {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
  margin-bottom: 0.75rem;
  font-size: 0.875rem;
  color: var(--c-gray);
}

.site-footer__contact-label {
  flex-shrink: 0;
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.675rem;
  color: var(--c-purple);
  border: 1px solid rgba(176, 38, 255, 0.35);
  padding: 0.1rem 0.35rem;
  margin-top: 0.15rem;
  line-height: 1.4;
}

.site-footer__contact a {
  color: var(--c-gray);
  word-break: break-all;
}

.site-footer__contact a:hover {
  color: var(--c-blue);
  text-decoration: none;
}

.site-footer__note {
  font-size: 0.75rem;
  color: var(--c-gray);
  font-family: var(--font-mono);
  border: 1px dashed var(--c-line);
  padding: 0.625rem 0.75rem;
  margin-top: 1rem;
}

.site-footer__bottom {
  border-top: 1px solid var(--c-line);
  background: var(--c-card);
  padding: 1rem 0;
}

.site-footer__bottom-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.site-footer__copyright,
.site-footer__icp {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--c-gray);
  margin: 0;
}

/* ===== 返回顶部 ===== */
.back-to-top {
  position: fixed;
  right: 1.25rem;
  bottom: 1.25rem;
  z-index: var(--z-fixed);
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(16, 16, 31, 0.9);
  border: 1px solid rgba(176, 38, 255, 0.45);
  color: var(--c-white);
  font-size: 1.25rem;
  line-height: 1;
  cursor: pointer;
  clip-path: polygon(8px 0, 100% 0, calc(100% - 8px) 100%, 0 100%);
  opacity: 0;
  visibility: hidden;
  transform: translateY(12px);
  transition:
    opacity var(--dur) var(--ease),
    transform var(--dur) var(--ease),
    background var(--dur) var(--ease),
    visibility var(--dur);
}

.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover {
  background: var(--c-purple);
  color: var(--c-black);
  border-color: var(--c-purple);
}

.back-to-top:focus-visible {
  clip-path: none;
  outline: 2px solid var(--c-blue);
  outline-offset: 2px;
}

.back-to-top__arrow {
  display: block;
  line-height: 1;
  transform: translateY(-1px);
}

/* ===== 响应式 ===== */
@media (max-width: 992px) {
  .grid--3,
  .grid--4 {
    grid-template-columns: repeat(2, 1fr);
  }

  .site-footer__grid {
    grid-template-columns: 1fr 1fr;
  }

  .site-footer__col--brand {
    grid-column: 1 / -1;
  }
}

@media (max-width: 768px) {
  .container {
    padding-inline: 1rem;
  }

  .section__head {
    flex-direction: column;
    gap: 0.75rem;
  }

  .section__side {
    flex: none;
    max-width: none;
    border-left: none;
    border-top: 2px solid var(--c-purple);
    padding-left: 0;
    padding-top: 0.5rem;
    margin-top: 0;
  }

  .site-header__topbar {
    display: none;
  }

  .site-header__masthead {
    grid-template-columns: 1fr auto;
    padding: 1rem 0;
  }

  .site-header__brand {
    grid-column: 1;
    justify-self: start;
  }

  .site-header__brand-mark {
    display: none;
  }

  .site-header__logo {
    font-size: 1.125rem;
  }

  .site-header__actions {
    grid-column: 2;
    justify-self: end;
  }

  .site-header__nav-toggle {
    display: inline-flex;
  }

  .site-header__action {
    padding: 0.5rem 0.875rem;
    font-size: 0.75rem;
  }

  .site-header__nav {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    max-height: 0;
    overflow-y: auto;
    border-bottom-color: transparent;
    box-shadow: 0 16px 32px rgba(0, 0, 0, 0.6);
    transition:
      max-height 0.4s var(--ease),
      border-color 0.4s var(--ease);
  }

  .site-header__nav[data-open] {
    max-height: 70vh;
    border-bottom-color: var(--c-line);
  }

  .site-header__nav-list {
    flex-direction: column;
    align-items: stretch;
  }

  .site-header__nav-link {
    padding: 0.875rem 1.25rem;
    border-left: 3px solid transparent;
  }

  .site-header__nav-link[aria-current="page"] {
    border-left-color: var(--c-orange);
  }
}

@media (max-width: 600px) {
  .grid--2,
  .grid--3,
  .grid--4 {
    grid-template-columns: 1fr;
  }

  .site-footer__grid {
    grid-template-columns: 1fr;
  }

  .site-footer__col--brand {
    grid-column: auto;
  }

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

@media (max-width: 360px) {
  .site-header__action {
    display: none;
  }
}