/* ============================================
   Clash免费下载站 v2 - 现代化样式
   ============================================ */

/* CSS Custom Properties (设计令牌) */
:root {
  /* 颜色系统 */
  --color-primary: #3b82f6;
  --color-primary-dark: #2563eb;
  --color-primary-light: #60a5fa;
  --color-primary-bg: rgba(59, 130, 246, 0.08);
  --color-accent: #ef4444;
  --color-accent-bg: rgba(239, 68, 68, 0.08);
  --color-success: #22c55e;
  --color-success-bg: rgba(34, 197, 94, 0.08);
  --color-warning: #f59e0b;
  --color-warning-bg: rgba(245, 158, 11, 0.08);

  /* 文字颜色 */
  --color-text: #1e293b;
  --color-text-secondary: #64748b;
  --color-text-muted: #94a3b8;

  /* 背景颜色 */
  --color-bg: #ffffff;
  --color-bg-secondary: #f8fafc;
  --color-bg-tertiary: #f1f5f9;

  /* 边框 */
  --color-border: #e2e8f0;
  --color-border-light: #f1f5f9;

  /* 阴影 */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.04);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.08), 0 8px 10px -6px rgba(0, 0, 0, 0.04);

  /* 间距 */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;
  --spacing-3xl: 4rem;

  /* 圆角 */
  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --radius-full: 9999px;

  /* 字体 */
  --font-sans: 'PingFang SC', 'Microsoft YaHei', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Fira Mono', 'Roboto Mono', Consolas, 'Andale Mono', monospace;

  /* 过渡 */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 350ms ease;

  /* 容器 */
  --container-max: 1200px;

  /* 头部高度 */
  --header-height: 70px;
}

/* 暗色模式变量 */
[data-theme="dark"] {
  --color-primary: #60a5fa;
  --color-primary-dark: #3b82f6;
  --color-primary-light: #93c5fd;
  --color-primary-bg: rgba(96, 165, 250, 0.12);
  --color-accent-bg: rgba(248, 113, 113, 0.12);
  --color-success-bg: rgba(74, 222, 128, 0.12);
  --color-warning-bg: rgba(251, 191, 36, 0.12);

  --color-text: #f1f5f9;
  --color-text-secondary: #94a3b8;
  --color-text-muted: #64748b;

  --color-bg: #0f172a;
  --color-bg-secondary: #1e293b;
  --color-bg-tertiary: #334155;

  --color-border: #334155;
  --color-border-light: #1e293b;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.4);
}

/* ============================================
   重置 & 基础样式
   ============================================ */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

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

body {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.7;
  color: var(--color-text);
  background-color: var(--color-bg);
  transition: background-color var(--transition-base), color var(--transition-base);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

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

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

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

ul, ol {
  list-style-position: inside;
}

/* ============================================
   布局
   ============================================ */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--spacing-lg);
}

/* ============================================
   头部导航
   ============================================ */
.header {
  position: sticky;
  top: 0;
  z-index: 100;
  background-color: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  backdrop-filter: blur(12px);
  background-color: rgba(255, 255, 255, 0.85);
  transition: background-color var(--transition-base);
}

[data-theme="dark"] .header {
  background-color: rgba(15, 23, 42, 0.85);
}

.header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: var(--header-height);
  gap: var(--spacing-xl);
}

.header__logo {
  display: flex;
  align-items: center;
  flex-shrink: 0;
}

.header__logo img {
  height: 40px;
  width: auto;
  object-fit: contain;
}

.header__logo-text {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--color-text);
  margin-left: var(--spacing-sm);
  white-space: nowrap;
}

/* 导航菜单 */
.nav {
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
}

.nav__link {
  display: flex;
  align-items: center;
  padding: var(--spacing-sm) var(--spacing-md);
  color: var(--color-text-secondary);
  font-weight: 500;
  font-size: 0.95rem;
  border-radius: var(--radius-md);
  transition: all var(--transition-fast);
  white-space: nowrap;
  position: relative;
}

.nav__link:hover,
.nav__link--active {
  color: var(--color-primary);
  background-color: var(--color-primary-bg);
}

/* 下拉菜单 */
.nav__item {
  position: relative;
}

.nav__dropdown {
  position: absolute;
  top: calc(100% + var(--spacing-sm));
  left: 50%;
  transform: translateX(-50%);
  min-width: 180px;
  background-color: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-xl);
  padding: var(--spacing-sm);
  opacity: 0;
  visibility: hidden;
  transform: translateX(-50%) translateY(8px);
  transition: all var(--transition-fast);
  z-index: 200;
}

.nav__item:hover .nav__dropdown {
  opacity: 1;
  visibility: visible;
  transform: translateX(-50%) translateY(0);
}

.nav__dropdown-link {
  display: block;
  padding: var(--spacing-sm) var(--spacing-md);
  color: var(--color-text-secondary);
  font-size: 0.9rem;
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
}

.nav__dropdown-link:hover {
  color: var(--color-primary);
  background-color: var(--color-primary-bg);
}

/* 主题切换按钮 */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background-color: var(--color-bg);
  color: var(--color-text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
  font-size: 1.1rem;
  flex-shrink: 0;
}

.theme-toggle:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background-color: var(--color-primary-bg);
}

/* 汉堡菜单按钮 */
.menu-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  width: 40px;
  height: 40px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background-color: var(--color-bg);
  cursor: pointer;
  gap: 5px;
  padding: 0;
  flex-shrink: 0;
}

.menu-toggle span {
  display: block;
  width: 20px;
  height: 2px;
  background-color: var(--color-text);
  border-radius: 1px;
  transition: all var(--transition-fast);
}

.menu-toggle.active span:nth-child(1) {
  transform: rotate(45deg) translate(5px, 5px);
}

.menu-toggle.active span:nth-child(2) {
  opacity: 0;
}

.menu-toggle.active span:nth-child(3) {
  transform: rotate(-45deg) translate(5px, -5px);
}

/* ============================================
   面包屑
   ============================================ */
.breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  padding: var(--spacing-lg) 0;
  font-size: 0.875rem;
  color: var(--color-text-muted);
  flex-wrap: wrap;
}

.breadcrumb__item {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.breadcrumb__item + .breadcrumb__item::before {
  content: "›";
  color: var(--color-text-muted);
}

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

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

.breadcrumb__current {
  color: var(--color-text);
  font-weight: 500;
}

/* ============================================
   Hero 区域
   ============================================ */
.hero {
  background: linear-gradient(135deg, var(--color-primary-bg) 0%, var(--color-bg-secondary) 100%);
  padding: var(--spacing-3xl) 0;
  text-align: center;
  border-bottom: 1px solid var(--color-border-light);
}

.hero__title {
  font-size: clamp(1.75rem, 4vw, 2.75rem);
  font-weight: 800;
  color: var(--color-text);
  margin-bottom: var(--spacing-md);
  line-height: 1.2;
}

.hero__desc {
  font-size: clamp(1rem, 2vw, 1.25rem);
  color: var(--color-text-secondary);
  max-width: 680px;
  margin-inline: auto;
  margin-bottom: var(--spacing-xl);
}

.hero__actions {
  display: flex;
  gap: var(--spacing-md);
  justify-content: center;
  flex-wrap: wrap;
}

/* ============================================
   按钮
   ============================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-sm);
  padding: 0.625rem 1.25rem;
  font-size: 0.95rem;
  font-weight: 600;
  line-height: 1.5;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
  text-decoration: none;
}

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

.btn--primary:hover {
  background-color: var(--color-primary-dark);
  color: #fff;
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn--secondary {
  background-color: var(--color-bg);
  color: var(--color-text);
  border: 1px solid var(--color-border);
}

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

.btn--sm {
  padding: 0.375rem 0.875rem;
  font-size: 0.85rem;
}

.btn--lg {
  padding: 0.875rem 1.75rem;
  font-size: 1.05rem;
}

/* ============================================
   特色卡片 (首页)
   ============================================ */
.features {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--spacing-xl);
  padding: var(--spacing-3xl) 0;
}

.feature-card {
  text-align: center;
  padding: var(--spacing-2xl);
  border-radius: var(--radius-xl);
  border: 1px solid var(--color-border-light);
  transition: border-color var(--transition-base), box-shadow var(--transition-base);
  will-change: transform;
}

.feature-card:hover {
  border-color: var(--color-primary);
  box-shadow: var(--shadow-lg);
  transform: translateY(-4px);
}

.feature-card__icon {
  width: 56px;
  height: 56px;
  border-radius: var(--radius-lg);
  background-color: var(--color-primary-bg);
  color: var(--color-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto var(--spacing-lg);
  font-size: 1.5rem;
}

.feature-card__title {
  font-size: 1.2rem;
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
  color: var(--color-text);
}

.feature-card__desc {
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-lg);
}

/* ============================================
   内容区域
   ============================================ */
.section {
  padding: var(--spacing-2xl) 0;
}

.section__title {
  font-size: 1.75rem;
  font-weight: 800;
  color: var(--color-text);
  margin-bottom: var(--spacing-md);
  padding-bottom: var(--spacing-sm);
  border-bottom: 3px solid var(--color-primary);
  display: inline-block;
}

.section__subtitle {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--color-text);
  margin: var(--spacing-xl) 0 var(--spacing-md);
}

.section p {
  margin-bottom: var(--spacing-md);
  color: var(--color-text);
}

.section ul,
.section ol {
  margin-bottom: var(--spacing-md);
  padding-left: var(--spacing-lg);
  list-style-position: outside;
}

.section li {
  margin-bottom: var(--spacing-xs);
}

/* 文本辅助类 */
.text-muted {
  color: var(--color-text-muted);
  font-size: 0.875rem;
}

/* 协议页面增强样式 */
.section h3 {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-text);
  margin: var(--spacing-lg) 0 var(--spacing-sm);
}

.footer__bottom a {
  color: var(--color-primary-light);
  text-decoration: none;
  transition: color 0.2s ease;
}

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

/* ============================================
   卡片网格
   ============================================ */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--spacing-xl);
  margin: var(--spacing-xl) 0;
}

.card {
  background-color: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-xl);
  overflow: hidden;
  transition: border-color var(--transition-base), box-shadow var(--transition-base);
  will-change: transform;
}

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

.card__body {
  padding: var(--spacing-xl);
}

.card__title {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: var(--spacing-md);
}

.card__text {
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-lg);
}

/* ============================================
   下载卡片
   ============================================ */
.download-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--spacing-xl);
  margin: var(--spacing-xl) 0;
}

.download-card {
  background-color: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-xl);
  padding: var(--spacing-xl);
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  transition: border-color var(--transition-base), box-shadow var(--transition-base);
  will-change: transform;
}

.download-card:hover {
  border-color: var(--color-primary);
  box-shadow: var(--shadow-lg);
  transform: translateY(-4px);
}

.download-card__img {
  width: 80px;
  height: 80px;
  object-fit: contain;
  margin-bottom: var(--spacing-md);
}

.download-card__title {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
  color: var(--color-text);
}

.download-card__badge {
  display: inline-block;
  background-color: var(--color-primary);
  color: #fff;
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.15rem 0.5rem;
  border-radius: var(--radius-full);
  margin-left: var(--spacing-xs);
  vertical-align: middle;
}

.download-card__desc {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-lg);
  flex-grow: 1;
}

.download-card__links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
  justify-content: center;
}

/* ============================================
   表格
   ============================================ */
.table-wrapper {
  overflow-x: auto;
  margin: var(--spacing-xl) 0;
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
}

.table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
}

.table th,
.table td {
  padding: var(--spacing-md) var(--spacing-lg);
  text-align: left;
  border-bottom: 1px solid var(--color-border-light);
}

.table th {
  background-color: var(--color-bg-secondary);
  font-weight: 700;
  color: var(--color-text);
  white-space: nowrap;
}

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

.table tr:hover td {
  background-color: var(--color-primary-bg);
}

/* ============================================
   FAQ 手风琴
   ============================================ */
.faq-list {
  margin: var(--spacing-xl) 0;
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.faq-item {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.faq-item:hover {
  border-color: var(--color-primary);
}

.faq-item__question {
  padding: var(--spacing-lg);
  background-color: var(--color-bg-secondary);
  font-weight: 600;
  font-size: 1rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--spacing-md);
  transition: background-color var(--transition-fast);
  color: var(--color-text);
  user-select: none;
}

.faq-item__question:hover {
  background-color: var(--color-bg-tertiary);
}

.faq-item__icon {
  flex-shrink: 0;
  width: 24px;
  height: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  color: var(--color-text-muted);
  transition: transform var(--transition-fast);
}

.faq-item.active .faq-item__icon {
  transform: rotate(45deg);
  color: var(--color-primary);
}

.faq-item__answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-slow), padding var(--transition-slow);
}

.faq-item.active .faq-item__answer {
  max-height: 2000px;
}

.faq-item__answer-inner {
  padding: var(--spacing-lg);
}

.faq-item__answer-inner p {
  margin-bottom: var(--spacing-md);
}

.faq-item__answer-inner ul,
.faq-item__answer-inner ol {
  margin-bottom: var(--spacing-md);
  padding-left: var(--spacing-lg);
}

/* ============================================
   教程步骤
   ============================================ */
.tutorial-steps {
  margin: var(--spacing-xl) 0;
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xl);
}

.tutorial-step {
  padding-bottom: var(--spacing-xl);
  border-bottom: 1px solid var(--color-border-light);
}

.tutorial-step:last-child {
  border-bottom: none;
  padding-bottom: 0;
}

.tutorial-step__title {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: var(--spacing-md);
}

/* ============================================
   提示框
   ============================================ */
.callout {
  padding: var(--spacing-lg);
  margin: var(--spacing-xl) 0;
  border-radius: var(--radius-md);
  border-left: 4px solid;
}

.callout--info {
  background-color: var(--color-primary-bg);
  border-color: var(--color-primary);
}

.callout--warning {
  background-color: var(--color-warning-bg);
  border-color: var(--color-warning);
}

.callout--danger {
  background-color: var(--color-accent-bg);
  border-color: var(--color-accent);
}

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

.callout p {
  margin-bottom: var(--spacing-sm);
}

.callout p:last-child {
  margin-bottom: 0;
}

/* ============================================
   价格卡片
   ============================================ */
.pricing-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: var(--spacing-xl);
  margin: var(--spacing-xl) 0;
}

.pricing-card {
  background-color: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-xl);
  padding: var(--spacing-2xl);
  text-align: center;
  transition: border-color var(--transition-base), box-shadow var(--transition-base), transform var(--transition-base);
  position: relative;
  will-change: transform;
}

.pricing-card--featured {
  border-color: var(--color-primary);
  border-width: 2px;
}

.pricing-card__badge {
  position: absolute;
  top: -12px;
  left: 50%;
  transform: translateX(-50%);
  background-color: var(--color-primary);
  color: #fff;
  font-size: 0.8rem;
  font-weight: 600;
  padding: 0.25rem 1rem;
  border-radius: var(--radius-full);
}

.pricing-card__title {
  font-size: 1.4rem;
  font-weight: 700;
  margin-bottom: var(--spacing-md);
}

.pricing-card__price {
  font-size: 2.5rem;
  font-weight: 800;
  color: var(--color-primary);
  margin-bottom: var(--spacing-lg);
}

.pricing-card__price span {
  font-size: 1rem;
  font-weight: 400;
  color: var(--color-text-muted);
}

.pricing-card__features {
  list-style: none;
  text-align: left;
  margin-bottom: var(--spacing-xl);
}

.pricing-card__features li {
  padding: var(--spacing-sm) 0;
  border-bottom: 1px solid var(--color-border-light);
  font-size: 0.95rem;
}

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

/* ============================================
   代码块
   ============================================ */
code {
  font-family: var(--font-mono);
  background-color: var(--color-bg-tertiary);
  color: var(--color-accent);
  padding: 0.15rem 0.4rem;
  border-radius: var(--radius-sm);
  font-size: 0.875em;
}

pre {
  font-family: var(--font-mono);
  background-color: var(--color-bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--spacing-lg);
  overflow-x: auto;
  margin: var(--spacing-xl) 0;
  line-height: 1.6;
}

pre code {
  background-color: transparent;
  color: var(--color-text);
  padding: 0;
  font-size: 0.875em;
}

/* ============================================
   联系信息
   ============================================ */
.contact-info {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
  margin-top: var(--spacing-md);
}

.contact-info p {
  font-size: 1rem;
}

/* ============================================
   页脚
   ============================================ */
.footer {
  background-color: var(--color-bg-secondary);
  border-top: 1px solid var(--color-border);
  padding: var(--spacing-3xl) 0 var(--spacing-xl);
  margin-top: var(--spacing-3xl);
}

[data-theme="dark"] .footer {
  background-color: #0c1222;
}

.footer__grid {
  display: grid;
  grid-template-columns: 2fr repeat(3, 1fr);
  gap: var(--spacing-2xl);
  margin-bottom: var(--spacing-2xl);
}

.footer__section-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: var(--spacing-lg);
}

.footer__section p {
  color: var(--color-text-secondary);
  font-size: 0.9rem;
  margin-bottom: var(--spacing-sm);
}

.footer__links {
  list-style: none;
}

.footer__links li {
  margin-bottom: var(--spacing-sm);
}

.footer__links a {
  color: var(--color-text-secondary);
  font-size: 0.9rem;
  transition: color var(--transition-fast);
}

.footer__links a:hover {
  color: var(--color-primary);
}

.footer__bottom {
  text-align: center;
  padding-top: var(--spacing-xl);
  border-top: 1px solid var(--color-border);
  color: var(--color-text-muted);
  font-size: 0.85rem;
}

/* ============================================
   返回顶部
   ============================================ */
.back-to-top {
  position: fixed;
  bottom: 24px;
  right: 24px;
  width: 44px;
  height: 44px;
  background-color: var(--color-primary);
  color: #fff;
  border: none;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: all var(--transition-base);
  z-index: 90;
  box-shadow: var(--shadow-lg);
  font-size: 1.2rem;
}

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

.back-to-top:hover {
  background-color: var(--color-primary-dark);
  transform: translateY(-2px);
}

/* ============================================
   动画（安全版本：元素默认可见，动画仅为增强）
   ============================================ */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* 等待动画的元素 - 默认仍可见，只是稍微淡一些 */
.animate-pending {
  opacity: 0.15;
  transition: opacity 0.3s ease;
}

/* 动画入场 */
.animate-in {
  opacity: 1 !important;
  animation: fadeInUp 0.5s ease-out;
}

/* 无JS fallback：确保元素始终可见 */
.no-js .animate-pending {
  opacity: 1;
}

/* ============================================
   自定义滚动条
   ============================================ */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--color-bg-secondary);
}

::-webkit-scrollbar-thumb {
  background: var(--color-text-muted);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--color-text-secondary);
}

/* ============================================
   响应式设计
   ============================================ */

/* 大平板 / 小桌面 */
@media (max-width: 1024px) {
  .features {
    grid-template-columns: repeat(2, 1fr);
  }

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

/* 平板 */
@media (max-width: 768px) {
  :root {
    --header-height: 60px;
  }

  .header__logo img {
    height: 36px;
    max-width: 120px;
  }

  /* 导航变汉堡菜单 */
  .menu-toggle {
    display: flex;
  }

  .nav {
    position: fixed;
    top: var(--header-height);
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--color-bg);
    flex-direction: column;
    align-items: stretch;
    padding: var(--spacing-lg);
    gap: 0;
    overflow-y: auto;
    transform: translateX(100%);
    transition: transform var(--transition-base);
    z-index: 99;
  }

  .nav.active {
    transform: translateX(0);
  }

  .nav__link {
    padding: var(--spacing-md);
    border-radius: 0;
    border-bottom: 1px solid var(--color-border-light);
  }

  .nav__dropdown {
    position: static;
    transform: none;
    opacity: 1;
    visibility: visible;
    box-shadow: none;
    border: none;
    padding: 0;
    padding-left: var(--spacing-lg);
    display: none;
  }

  .nav__item.dropdown-open .nav__dropdown {
    display: block;
  }

  .features {
    grid-template-columns: 1fr;
  }

  .hero {
    padding: var(--spacing-2xl) 0;
  }

  .section__title {
    font-size: 1.5rem;
  }

  .footer__grid {
    grid-template-columns: 1fr;
    gap: var(--spacing-xl);
  }

  .pricing-grid {
    grid-template-columns: 1fr;
  }
}

/* 手机 */
@media (max-width: 480px) {
  .container {
    padding-inline: var(--spacing-md);
  }

  .header__logo img {
    height: 32px;
    max-width: 100px;
  }

  .hero__title {
    font-size: 1.5rem;
  }

  .download-grid,
  .card-grid {
    grid-template-columns: 1fr;
  }

  .download-card__links {
    flex-direction: column;
    width: 100%;
  }

  .download-card__links .btn {
    width: 100%;
  }
}