/* =============================================
   蔚蓝守护 - 海洋生态环境保护公益宣传网站
   统一样式表
   ============================================= */

/* CSS 变量 - 全站配色规范 */
:root {
  --color-primary: #0F4C81;        /* 深海蓝 - 主色 */
  --color-primary-dark: #0a3559;   /* 深海蓝 - 悬浮加深 */
  --color-secondary: #4ECDC4;      /* 浅海青 - 辅助色 */
  --color-accent: #FF9F1C;         /* 珊瑚浅橙 - 强调色 */
  --color-accent-dark: #e08a0e;    /* 珊瑚浅橙 - 悬浮加深 */
  --color-white: #FFFFFF;          /* 纯白底 */
  --color-bg-soft: #F4F9FB;        /* 软背景 */
  --color-text: #1f2d3d;           /* 主文本 */
  --color-text-soft: #5a6c7d;      /* 次要文本 */
  --color-border: #e3edf2;         /* 边框 */
  --shadow-sm: 0 2px 6px rgba(15, 76, 129, 0.08);
  --shadow-md: 0 8px 24px rgba(15, 76, 129, 0.12);
  --shadow-lg: 0 16px 40px rgba(15, 76, 129, 0.16);
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --transition: 0.3s ease;
  --font-family: "PingFang SC", "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial, sans-serif;
}

/* 全局重置 */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-family);
  color: var(--color-text);
  background-color: var(--color-white);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

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

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

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

h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  color: var(--color-primary);
  line-height: 1.3;
}

.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 24px;
}

/* =============================================
   导航栏
   ============================================= */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--color-white);
  box-shadow: var(--shadow-sm);
  border-bottom: 3px solid var(--color-secondary);
}

.nav-wrap {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
}

.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 22px;
  font-weight: 700;
  color: var(--color-primary);
}

.logo-icon {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--color-primary), var(--color-secondary));
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-white);
  font-size: 20px;
  font-weight: 700;
}

.nav-menu {
  display: flex;
  gap: 32px;
  list-style: none;
  align-items: center;
}

.nav-menu a {
  color: var(--color-text);
  font-size: 15px;
  font-weight: 500;
  padding: 6px 4px;
  position: relative;
  transition: color var(--transition);
}

.nav-menu a::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--color-accent);
  transition: width var(--transition);
}

.nav-menu a:hover,
.nav-menu a.active {
  color: var(--color-primary);
}

.nav-menu a:hover::after,
.nav-menu a.active::after {
  width: 100%;
}

.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 8px;
}

.nav-toggle span {
  display: block;
  width: 26px;
  height: 3px;
  background: var(--color-primary);
  border-radius: 2px;
  transition: var(--transition);
}

.nav-toggle.active span:nth-child(1) {
  transform: translateY(8px) rotate(45deg);
}
.nav-toggle.active span:nth-child(2) {
  opacity: 0;
}
.nav-toggle.active span:nth-child(3) {
  transform: translateY(-8px) rotate(-45deg);
}

/* =============================================
   全屏 Banner
   ============================================= */
.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  background: linear-gradient(135deg, rgba(15, 76, 129, 0.85), rgba(78, 205, 196, 0.75)),
              url('https://trae-api-cn.mchost.guru/api/ide/v1/text_to_image?prompt=underwater%20ocean%20coral%20reef%20sunlight%20rays%20blue%20water%20marine%20life&image_size=landscape_16_9') center/cover no-repeat;
  color: var(--color-white);
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at 30% 50%, rgba(255, 159, 28, 0.18), transparent 60%);
  pointer-events: none;
}

.hero-content {
  position: relative;
  max-width: 880px;
  padding: 0 24px;
  animation: fadeUp 1s ease;
}

.hero-title {
  font-size: 60px;
  font-weight: 800;
  letter-spacing: 4px;
  margin-bottom: 20px;
  color: var(--color-white);
  text-shadow: 0 4px 24px rgba(0, 0, 0, 0.25);
}

.hero-subtitle {
  font-size: 22px;
  font-weight: 400;
  margin-bottom: 12px;
  opacity: 0.95;
  letter-spacing: 1px;
}

.hero-tagline {
  font-size: 16px;
  margin-bottom: 40px;
  opacity: 0.85;
  line-height: 1.8;
}

.btn {
  display: inline-block;
  padding: 14px 36px;
  border-radius: 30px;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition);
  border: 2px solid transparent;
  text-align: center;
  letter-spacing: 1px;
}

.btn-primary {
  background: var(--color-accent);
  color: var(--color-white);
  box-shadow: 0 6px 18px rgba(255, 159, 28, 0.4);
}

.btn-primary:hover {
  background: var(--color-accent-dark);
  color: var(--color-white);
  transform: translateY(-3px);
  box-shadow: 0 10px 24px rgba(255, 159, 28, 0.5);
}

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

.btn-outline:hover {
  background: var(--color-primary);
  color: var(--color-white);
  transform: translateY(-3px);
}

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

.btn-white:hover {
  background: var(--color-accent);
  color: var(--color-white);
  border-color: var(--color-accent);
  transform: translateY(-3px);
}

.scroll-down {
  position: absolute;
  bottom: 32px;
  left: 50%;
  transform: translateX(-50%);
  color: var(--color-white);
  font-size: 14px;
  letter-spacing: 2px;
  opacity: 0.85;
  animation: bounce 2s infinite;
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(40px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes bounce {
  0%, 100% { transform: translate(-50%, 0); }
  50% { transform: translate(-50%, -10px); }
}

/* =============================================
   通用板块
   ============================================= */
.section {
  padding: 96px 0;
}

.section-soft {
  background: var(--color-bg-soft);
}

.section-header {
  text-align: center;
  margin-bottom: 56px;
}

.section-eyebrow {
  display: inline-block;
  font-size: 14px;
  color: var(--color-accent);
  font-weight: 600;
  letter-spacing: 3px;
  text-transform: uppercase;
  margin-bottom: 12px;
}

.section-title {
  font-size: 40px;
  color: var(--color-primary);
  margin-bottom: 16px;
}

.section-subtitle {
  font-size: 17px;
  color: var(--color-text-soft);
  max-width: 680px;
  margin: 0 auto;
}

.divider {
  width: 60px;
  height: 4px;
  background: var(--color-accent);
  border-radius: 2px;
  margin: 18px auto 0;
}

/* =============================================
   卡片网格
   ============================================= */
.card-grid {
  display: grid;
  gap: 32px;
}

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

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

.card {
  background: var(--color-white);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: all var(--transition);
  display: flex;
  flex-direction: column;
  cursor: pointer;
  text-decoration: none;
  color: inherit;
  border: 1px solid var(--color-border);
}

.card:hover {
  transform: translateY(-8px) scale(1.02);
  box-shadow: var(--shadow-lg);
  border-color: var(--color-secondary);
  color: inherit;
}

.card-image {
  width: 100%;
  height: 220px;
  overflow: hidden;
  position: relative;
}

.card-image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.6s ease;
}

.card:hover .card-image img {
  transform: scale(1.08);
}

.card-image::after {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, transparent 50%, rgba(15, 76, 129, 0.5));
}

.card-body {
  padding: 28px 24px;
  flex: 1;
  display: flex;
  flex-direction: column;
}

.card-tag {
  display: inline-block;
  padding: 4px 12px;
  background: rgba(78, 205, 196, 0.15);
  color: var(--color-primary);
  font-size: 12px;
  border-radius: 20px;
  margin-bottom: 12px;
  font-weight: 600;
  letter-spacing: 1px;
  align-self: flex-start;
}

.card-title {
  font-size: 22px;
  margin-bottom: 12px;
  color: var(--color-primary);
}

.card-desc {
  color: var(--color-text-soft);
  font-size: 15px;
  line-height: 1.7;
  flex: 1;
  margin-bottom: 16px;
}

.card-arrow {
  color: var(--color-accent);
  font-weight: 600;
  font-size: 14px;
  letter-spacing: 1px;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: gap var(--transition);
}

.card:hover .card-arrow {
  gap: 12px;
}

/* =============================================
   栏目入口大卡片
   ============================================= */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 32px;
}

.feature-card {
  position: relative;
  border-radius: var(--radius-lg);
  overflow: hidden;
  height: 380px;
  cursor: pointer;
  transition: transform var(--transition);
  box-shadow: var(--shadow-md);
  text-decoration: none;
  color: var(--color-white);
}

.feature-card:hover {
  transform: translateY(-8px) scale(1.02);
  color: var(--color-white);
}

.feature-card img {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  z-index: 1;
  transition: transform 0.6s ease;
}

.feature-card:hover img {
  transform: scale(1.08);
}

.feature-card::before {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, rgba(15, 76, 129, 0.3) 0%, rgba(15, 76, 129, 0.85) 100%);
  z-index: 2;
}

.feature-content {
  position: relative;
  z-index: 3;
  height: 100%;
  padding: 32px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
}

.feature-icon {
  font-size: 36px;
  margin-bottom: 12px;
  display: inline-block;
  width: 64px;
  height: 64px;
  border-radius: 50%;
  background: rgba(255, 159, 28, 0.85);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-white);
  font-size: 32px;
  margin-bottom: 16px;
}

.feature-title {
  font-size: 26px;
  color: var(--color-white);
  margin-bottom: 10px;
}

.feature-desc {
  font-size: 14px;
  opacity: 0.9;
  margin-bottom: 16px;
  line-height: 1.7;
}

.feature-link {
  font-size: 14px;
  font-weight: 600;
  letter-spacing: 2px;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  color: var(--color-accent);
}

.feature-card:hover .feature-link {
  gap: 14px;
}

/* =============================================
   数据展示
   ============================================= */
.stats-section {
  background: linear-gradient(135deg, var(--color-primary) 0%, #1a5b8f 100%);
  color: var(--color-white);
  padding: 80px 0;
  position: relative;
  overflow: hidden;
}

.stats-section::before {
  content: '';
  position: absolute;
  width: 400px;
  height: 400px;
  border-radius: 50%;
  background: rgba(78, 205, 196, 0.15);
  top: -200px;
  right: -200px;
}

.stats-section::after {
  content: '';
  position: absolute;
  width: 300px;
  height: 300px;
  border-radius: 50%;
  background: rgba(255, 159, 28, 0.1);
  bottom: -150px;
  left: -150px;
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 32px;
  text-align: center;
  position: relative;
  z-index: 1;
}

.stat-item {
  padding: 24px 12px;
}

.stat-number {
  font-size: 52px;
  font-weight: 800;
  color: var(--color-accent);
  margin-bottom: 8px;
  letter-spacing: 1px;
}

.stat-label {
  font-size: 16px;
  opacity: 0.95;
  letter-spacing: 1px;
}

/* =============================================
   资讯列表
   ============================================= */
.news-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 32px;
}

.news-card {
  background: var(--color-white);
  padding: 32px 28px;
  border-radius: var(--radius-md);
  border-left: 4px solid var(--color-secondary);
  box-shadow: var(--shadow-sm);
  transition: all var(--transition);
}

.news-card:hover {
  transform: translateX(6px);
  box-shadow: var(--shadow-md);
  border-left-color: var(--color-accent);
}

.news-date {
  font-size: 13px;
  color: var(--color-text-soft);
  margin-bottom: 8px;
  letter-spacing: 1px;
}

.news-title {
  font-size: 18px;
  color: var(--color-primary);
  margin-bottom: 10px;
}

.news-excerpt {
  color: var(--color-text-soft);
  font-size: 14px;
  line-height: 1.7;
}

/* =============================================
   二级页面 Banner
   ============================================= */
.page-banner {
  position: relative;
  height: 360px;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  color: var(--color-white);
  background: linear-gradient(135deg, rgba(15, 76, 129, 0.85), rgba(78, 205, 196, 0.7)),
              url('https://trae-api-cn.mchost.guru/api/ide/v1/text_to_image?prompt=ocean%20sea%20waves%20blue%20water%20sunlight&image_size=landscape_16_9') center/cover no-repeat;
  overflow: hidden;
}

.page-banner.banner-pollution {
  background: linear-gradient(135deg, rgba(15, 76, 129, 0.85), rgba(78, 205, 196, 0.6)),
              url('https://trae-api-cn.mchost.guru/api/ide/v1/text_to_image?prompt=polluted%20ocean%20plastic%20waste%20floating%20in%20sea&image_size=landscape_16_9') center/cover no-repeat;
}

.page-banner.banner-species {
  background: linear-gradient(135deg, rgba(15, 76, 129, 0.85), rgba(78, 205, 196, 0.7)),
              url('https://trae-api-cn.mchost.guru/api/ide/v1/text_to_image?prompt=sea%20turtle%20dolphin%20coral%20reef%20underwater%20marine%20life&image_size=landscape_16_9') center/cover no-repeat;
}

.page-banner.banner-action {
  background: linear-gradient(135deg, rgba(15, 76, 129, 0.8), rgba(255, 159, 28, 0.55)),
              url('https://trae-api-cn.mchost.guru/api/ide/v1/text_to_image?prompt=volunteers%20cleaning%20beach%20hands%20together%20sunlight&image_size=landscape_16_9') center/cover no-repeat;
}

.page-banner-content {
  position: relative;
  max-width: 800px;
  padding: 0 24px;
  animation: fadeUp 0.8s ease;
}

.page-banner h1 {
  font-size: 48px;
  color: var(--color-white);
  margin-bottom: 16px;
  letter-spacing: 4px;
  text-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
}

.page-banner p {
  font-size: 17px;
  opacity: 0.95;
  line-height: 1.8;
}

/* 面包屑 */
.breadcrumb {
  padding: 18px 0;
  background: var(--color-bg-soft);
  font-size: 14px;
  color: var(--color-text-soft);
}

.breadcrumb a {
  color: var(--color-text-soft);
}

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

.breadcrumb .current {
  color: var(--color-primary);
  font-weight: 600;
}

.breadcrumb-sep {
  margin: 0 10px;
  color: var(--color-text-soft);
}

/* =============================================
   二级页面科普区
   ============================================= */
.info-block {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 56px;
  align-items: center;
  margin-bottom: 64px;
}

.info-block.reverse {
  direction: rtl;
}

.info-block.reverse > * {
  direction: ltr;
}

.info-image {
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-md);
}

.info-image img {
  width: 100%;
  height: 360px;
  object-fit: cover;
  transition: transform 0.6s ease;
}

.info-image:hover img {
  transform: scale(1.05);
}

.info-content h3 {
  font-size: 28px;
  margin-bottom: 18px;
  color: var(--color-primary);
}

.info-content p {
  color: var(--color-text-soft);
  font-size: 16px;
  line-height: 1.9;
  margin-bottom: 14px;
}

/* =============================================
   三级详情页
   ============================================= */
.article-hero {
  position: relative;
  height: 320px;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  color: var(--color-white);
  background: linear-gradient(135deg, rgba(15, 76, 129, 0.85), rgba(78, 205, 196, 0.65)),
              url('https://trae-api-cn.mchost.guru/api/ide/v1/text_to_image?prompt=deep%20blue%20ocean%20underwater%20coral%20reef%20sunlight%20rays&image_size=landscape_16_9') center/cover no-repeat;
  margin-bottom: 0;
}

.article-hero h1 {
  font-size: 44px;
  color: var(--color-white);
  letter-spacing: 3px;
  text-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
  margin-bottom: 12px;
}

.article-hero p {
  font-size: 16px;
  opacity: 0.9;
}

.article-wrap {
  max-width: 920px;
  margin: 0 auto;
  padding: 64px 24px 0;
}

.article-section {
  margin-bottom: 48px;
}

.article-section h2 {
  font-size: 28px;
  color: var(--color-primary);
  margin-bottom: 20px;
  padding-left: 16px;
  border-left: 4px solid var(--color-accent);
}

.article-section h3 {
  font-size: 20px;
  color: var(--color-primary);
  margin: 28px 0 14px;
}

.article-section p {
  color: var(--color-text);
  font-size: 16px;
  line-height: 1.9;
  margin-bottom: 16px;
}

.article-section ul,
.article-section ol {
  padding-left: 24px;
  margin-bottom: 18px;
}

.article-section li {
  margin-bottom: 10px;
  color: var(--color-text);
  line-height: 1.8;
}

.article-figure {
  margin: 32px 0;
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-md);
}

.article-figure img {
  width: 100%;
  height: 360px;
  object-fit: cover;
}

.article-figure figcaption {
  background: var(--color-bg-soft);
  padding: 14px 20px;
  font-size: 14px;
  color: var(--color-text-soft);
  text-align: center;
  font-style: italic;
}

.callout {
  display: flex;
  gap: 16px;
  padding: 24px 28px;
  background: linear-gradient(135deg, rgba(78, 205, 196, 0.1), rgba(15, 76, 129, 0.05));
  border-left: 4px solid var(--color-secondary);
  border-radius: var(--radius-sm);
  margin: 28px 0;
}

.callout-icon {
  font-size: 28px;
  flex-shrink: 0;
}

.callout-text {
  color: var(--color-text);
  font-size: 15px;
  line-height: 1.8;
}

.callout-text strong {
  color: var(--color-primary);
}

.data-strip {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
  margin: 32px 0;
}

.data-tile {
  background: var(--color-bg-soft);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 24px 16px;
  text-align: center;
}

.data-tile-num {
  font-size: 32px;
  font-weight: 800;
  color: var(--color-accent);
  margin-bottom: 6px;
}

.data-tile-label {
  font-size: 14px;
  color: var(--color-text-soft);
}

/* 行动建议区 */
.action-section {
  background: linear-gradient(135deg, var(--color-primary) 0%, #1a5b8f 100%);
  color: var(--color-white);
  padding: 56px 0;
  margin-top: 48px;
  position: relative;
  overflow: hidden;
}

.action-section::before {
  content: '';
  position: absolute;
  width: 300px;
  height: 300px;
  border-radius: 50%;
  background: rgba(255, 159, 28, 0.12);
  top: -150px;
  right: -150px;
}

.action-section h2 {
  text-align: center;
  color: var(--color-white);
  font-size: 32px;
  margin-bottom: 40px;
  position: relative;
}

.action-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  position: relative;
}

.action-card {
  background: rgba(255, 255, 255, 0.08);
  backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.15);
  padding: 28px 24px;
  border-radius: var(--radius-md);
  transition: all var(--transition);
}

.action-card:hover {
  background: rgba(255, 255, 255, 0.15);
  transform: translateY(-6px);
  border-color: var(--color-accent);
}

.action-card-icon {
  font-size: 36px;
  margin-bottom: 14px;
  display: block;
}

.action-card h3 {
  font-size: 18px;
  color: var(--color-accent);
  margin-bottom: 10px;
}

.action-card p {
  font-size: 14px;
  opacity: 0.9;
  line-height: 1.8;
}

/* 返回按钮区 */
.nav-buttons {
  display: flex;
  justify-content: center;
  gap: 16px;
  padding: 56px 0 80px;
  flex-wrap: wrap;
}

.btn-back {
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

/* =============================================
   页脚
   ============================================= */
.site-footer {
  background: #0a2a47;
  color: rgba(255, 255, 255, 0.8);
  padding: 56px 0 24px;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: 48px;
  margin-bottom: 40px;
}

.footer-col h4 {
  color: var(--color-white);
  font-size: 16px;
  margin-bottom: 18px;
  letter-spacing: 1px;
}

.footer-col p {
  font-size: 14px;
  line-height: 1.8;
  margin-bottom: 12px;
  opacity: 0.85;
}

.footer-col ul {
  list-style: none;
}

.footer-col ul li {
  margin-bottom: 10px;
}

.footer-col ul li a {
  color: rgba(255, 255, 255, 0.7);
  font-size: 14px;
  transition: color var(--transition);
}

.footer-col ul li a:hover {
  color: var(--color-accent);
}

.footer-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 22px;
  font-weight: 700;
  color: var(--color-white);
  margin-bottom: 16px;
}

.footer-bottom {
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  padding-top: 24px;
  text-align: center;
  font-size: 13px;
  opacity: 0.7;
}

/* =============================================
   回到顶部
   ============================================= */
.back-to-top {
  position: fixed;
  bottom: 32px;
  right: 32px;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: var(--color-primary);
  color: var(--color-white);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 22px;
  cursor: pointer;
  border: none;
  box-shadow: var(--shadow-md);
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition);
  z-index: 50;
}

.back-to-top.show {
  opacity: 1;
  visibility: visible;
}

.back-to-top:hover {
  background: var(--color-accent);
  transform: translateY(-4px);
}

/* =============================================
   响应式
   ============================================= */
@media (max-width: 1023px) {
  .hero-title { font-size: 48px; }
  .section-title { font-size: 34px; }
  .page-banner h1 { font-size: 40px; }
  .article-hero h1 { font-size: 36px; }
  .feature-grid,
  .card-grid.cols-3,
  .news-grid,
  .action-grid { grid-template-columns: repeat(2, 1fr); }
  .stats-grid { grid-template-columns: repeat(2, 1fr); gap: 24px; }
  .footer-grid { grid-template-columns: 1fr 1fr; gap: 32px; }
  .info-block { grid-template-columns: 1fr; gap: 32px; }
  .info-block.reverse { direction: ltr; }
}

@media (max-width: 767px) {
  .nav-toggle { display: flex; }
  .nav-menu {
    position: fixed;
    top: 72px;
    left: 0;
    right: 0;
    background: var(--color-white);
    flex-direction: column;
    gap: 0;
    padding: 0;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.4s ease;
    box-shadow: var(--shadow-md);
  }
  .nav-menu.open {
    max-height: 600px;
  }
  .nav-menu li {
    width: 100%;
    border-bottom: 1px solid var(--color-border);
  }
  .nav-menu a {
    display: block;
    padding: 18px 24px;
  }
  .nav-menu a::after { display: none; }

  .hero { min-height: 90vh; }
  .hero-title { font-size: 36px; letter-spacing: 2px; }
  .hero-subtitle { font-size: 17px; }
  .hero-tagline { font-size: 14px; }

  .section { padding: 64px 0; }
  .section-title { font-size: 28px; }
  .page-banner { height: 280px; }
  .page-banner h1 { font-size: 30px; letter-spacing: 2px; }
  .article-hero { height: 240px; }
  .article-hero h1 { font-size: 26px; }

  .feature-grid,
  .card-grid.cols-3,
  .card-grid.cols-2,
  .news-grid,
  .action-grid { grid-template-columns: 1fr; }

  .stats-grid { grid-template-columns: 1fr 1fr; }
  .stat-number { font-size: 38px; }

  .footer-grid { grid-template-columns: 1fr; gap: 28px; }

  .container { padding: 0 18px; }
  .article-wrap { padding: 40px 18px 0; }

  .data-strip { grid-template-columns: 1fr; }

  .nav-buttons { padding: 40px 18px 56px; }
  .nav-buttons .btn { flex: 1; min-width: 140px; }
}

/* =============================================
   滚动渐入动画
   ============================================= */
.reveal {
  opacity: 0;
  transform: translateY(28px);
  transition: opacity 0.7s ease, transform 0.7s ease;
}

.reveal-show {
  opacity: 1;
  transform: translateY(0);
}

.reveal[data-delay="1"] { transition-delay: 0.08s; }
.reveal[data-delay="2"] { transition-delay: 0.16s; }
.reveal[data-delay="3"] { transition-delay: 0.24s; }
.reveal[data-delay="4"] { transition-delay: 0.32s; }