:root {
  --bg: #f9fafb;
  --fg: #1f2937;
  --card-bg: #ffffff;
  --card-hover: #f3f4f6;
  --accent: #3b82f6;
  --border: #e5e7eb;
  --header-bg: rgba(249, 250, 251, 0.9);
  --header-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

html[data-theme="dark"] {
  --bg: #0f172a;
  --fg: #e2e8f0;
  --card-bg: #1e293b;
  --card-hover: #334155;
  --accent: #3b82f6;
  --border: #334155;
  --header-bg: rgba(15, 23, 42, 0.9);
}

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

body {
  background: var(--bg);
  color: var(--fg);
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  padding-top: 4rem; /* 为固定header留出空间 */
}

/* ===== 头部样式 ===== */
header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 2rem;
  max-width: 100%;
  width: 100%;
  margin: 0 auto;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  background: var(--header-bg);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 1000;
  box-shadow: var(--header-shadow);
  transition: background-color 0.3s;
}

.header-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
}

.title {
  font-size: 1.5rem;
  font-weight: 700;
  cursor: pointer;
  position: relative;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.about-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.5rem 1rem;
  border-radius: 0.5rem;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--fg);
  background-color: var(--card-bg);
  border: 1px solid var(--border);
  text-decoration: none;
  transition: all 0.2s;
}

.about-btn:hover {
  background-color: var(--card-hover);
  transform: translateY(-2px);
}

.toggle-btn {
  cursor: pointer;
  border: none;
  background: transparent;
  font-size: 1.5rem;
  line-height: 1;
  color: var(--fg);
  transition: transform 0.2s;
}

.toggle-btn:hover {
  transform: rotate(20deg);
}

/* ===== 下拉菜单样式 ===== */
.dropdown-menu {
  position: absolute;
  top: 100%;
  left: 50%;
  transform: translateX(-50%);
  width: 180px;
  z-index: 1100;
  visibility: hidden;
  opacity: 0;
  transition: visibility 0s linear 1s, opacity 0.3s;
  margin-top: 0.5rem;
}

.title:hover .dropdown-menu {
  visibility: visible;
  opacity: 1;
  transition-delay: 1s; /* 悬停1秒后显示 */
}

.dropdown-content {
  background-color: var(--card-bg);
  border-radius: 0.5rem;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.dropdown-item {
  padding: 0.75rem 1rem;
  color: var(--fg);
  text-decoration: none;
  transition: background-color 0.2s, color 0.2s;
  text-align: center;
  font-size: 0.9rem;
  border-bottom: 1px solid var(--border);
}

.dropdown-item:last-child {
  border-bottom: none;
}

.dropdown-item:hover {
  background-color: var(--card-hover);
  color: var(--accent);
}

/* 添加三角形指示器 */
.dropdown-menu::before {
  content: '';
  position: absolute;
  top: -8px;
  left: 50%;
  transform: translateX(-50%);
  border-left: 8px solid transparent;
  border-right: 8px solid transparent;
  border-bottom: 8px solid var(--card-bg);
  z-index: 1;
}

/* ===== 主体内容样式 ===== */
main {
  flex: 1;
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem;
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

.category {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.category-title {
  font-size: 1.25rem;
  font-weight: 600;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 0.5rem;
  color: var(--accent);
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(min(100%, calc((100% - 5 * 1.25rem) / 6)), 1fr));
  gap: 1.25rem;
}

.card {
  background: var(--card-bg);
  border-radius: 0.75rem;
  padding: 1.25rem;
  text-decoration: none;
  color: var(--fg);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.75rem;
  transition: background 0.2s, transform 0.2s;
  box-shadow: 0 1px 2px rgba(0,0,0,0.05);
  aspect-ratio: 3/2;
}

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

.card svg {
  width: 32px;
  height: 32px;
  fill: var(--accent);
}

/* ===== 页脚样式 ===== */
footer {
  text-align: center;
  padding: 1rem 0 2rem;
  font-size: 0.875rem;
  color: var(--fg);
  margin-top: 2rem;
  position: relative;
}

.footer-divider {
  height: 1px;
  background: linear-gradient(to right, transparent, var(--border), transparent);
  width: 80%;
  max-width: 800px;
  margin: 0 auto 1.5rem;
}

.footer-content {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
}

.footer-info {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 1rem;
  margin-bottom: 0.5rem;
}

.footer-info a {
  color: var(--fg);
  text-decoration: none;
  transition: color 0.2s, transform 0.2s;
  display: inline-flex;
  align-items: center;
}

.footer-info a:hover {
  color: var(--accent);
  transform: translateY(-2px);
}

.footer-dot {
  color: var(--border);
  margin: 0 0.5rem;
}

.footer-line a {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--fg);
  text-decoration: none;
  padding: 0.5rem 1rem;
  border-radius: 2rem;
  background-color: var(--card-bg);
  box-shadow: 0 1px 3px rgba(0,0,0,0.1);
  transition: all 0.3s ease;
}

.footer-line a:hover {
  background-color: var(--card-hover);
  transform: translateY(-2px);
  box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}

.footer-icon {
  width: 16px;
  height: 16px;
}

/* ===== 响应式布局 ===== */
@media (prefers-color-scheme: dark) {
  html[data-theme="auto"] {
    --bg: #0f172a;
    --fg: #e2e8f0;
    --card-bg: #1e293b;
    --card-hover: #334155;
    --border: #334155;
    --header-bg: rgba(15, 23, 42, 0.9);
  }
}

@media (max-width: 1200px) {
  .card-grid {
    grid-template-columns: repeat(auto-fill, minmax(min(100%, calc((100% - 4 * 1.25rem) / 5)), 1fr));
  }
}

@media (max-width: 992px) {
  .card-grid {
    grid-template-columns: repeat(auto-fill, minmax(min(100%, calc((100% - 3 * 1.25rem) / 4)), 1fr));
  }
}

@media (max-width: 768px) {
  .card-grid {
    grid-template-columns: repeat(auto-fill, minmax(min(100%, calc((100% - 2 * 1.25rem) / 3)), 1fr));
  }
  header {
    padding: 0.75rem 1rem;
  }
  body {
    padding-top: 3.5rem;
  }
}

@media (max-width: 576px) {
  .card-grid {
    grid-template-columns: repeat(auto-fill, minmax(min(100%, calc((100% - 1.25rem) / 2)), 1fr));
  }
}

@media (max-width: 375px) {
  .card-grid {
    grid-template-columns: 1fr;
  }
}