:root {
    --bg-color: #f8fafc;
    --nav-bg: rgba(255, 255, 255, 0.98);
    --card-bg: #ffffff;
    --card-hover: #f1f5f9;
    --text-primary: #0f172a;
    --text-secondary: #334155;
    --text-muted: #64748b;
    --accent-color: #0284c7;
    --accent-icon: #0369a1;
    --accent-light: #e0f2fe;
    --border-color: #cbd5e1;

    --tag-chat-bg: #fee2e2;
    --tag-chat-text: #991b1b;
    --tag-multi-bg: #dcfce7;
    --tag-multi-text: #166534;
    --tag-media-bg: #fef9c3;
    --tag-media-text: #854d0e;

    --shadow-sm: 0 1px 3px rgba(15, 23, 42, 0.08);
    --shadow-hover: 0 10px 15px -3px rgba(15, 23, 42, 0.12);
    --focus-ring: 0 0 0 3px rgba(2, 132, 199, 0.35);

    --header-bg: linear-gradient(180deg, #e0f2fe 0%, var(--bg-color) 100%);
    --summary-bg: #f1f5f9;
}

/* 暗色主题 / 夜间模式 (Dark Mode) */
[data-theme="dark"] {
    --bg-color: #0f172a;
    --nav-bg: rgba(15, 23, 42, 0.95);
    --card-bg: #1e293b;
    --card-hover: #334155;
    --text-primary: #f8fafc;
    --text-secondary: #cbd5e1;
    --text-muted: #94a3b8;
    --accent-color: #38bdf8;
    --accent-icon: #38bdf8;
    --accent-light: rgba(56, 189, 248, 0.15);
    --border-color: #334155;

    --tag-chat-bg: rgba(239, 68, 68, 0.2);
    --tag-chat-text: #fca5a5;
    --tag-multi-bg: rgba(34, 197, 94, 0.2);
    --tag-multi-text: #86efac;
    --tag-media-bg: rgba(234, 179, 8, 0.2);
    --tag-media-text: #fde047;

    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
    --shadow-hover: 0 10px 15px -3px rgba(0, 0, 0, 0.5);

    --header-bg: linear-gradient(180deg, #1e293b 0%, var(--bg-color) 100%);
    --summary-bg: #334155;
}

/* 自动跟随系统暗色偏好 */
@media (prefers-color-scheme: dark) {
    :root:not([data-theme="light"]) {
        --bg-color: #0f172a;
        --nav-bg: rgba(15, 23, 42, 0.95);
        --card-bg: #1e293b;
        --card-hover: #334155;
        --text-primary: #f8fafc;
        --text-secondary: #cbd5e1;
        --text-muted: #94a3b8;
        --accent-color: #38bdf8;
        --accent-icon: #38bdf8;
        --accent-light: rgba(56, 189, 248, 0.15);
        --border-color: #334155;

        --tag-chat-bg: rgba(239, 68, 68, 0.2);
        --tag-chat-text: #fca5a5;
        --tag-multi-bg: rgba(34, 197, 94, 0.2);
        --tag-multi-text: #86efac;
        --tag-media-bg: rgba(234, 179, 8, 0.2);
        --tag-media-text: #fde047;

        --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
        --shadow-hover: 0 10px 15px -3px rgba(0, 0, 0, 0.5);

        --header-bg: linear-gradient(180deg, #1e293b 0%, var(--bg-color) 100%);
        --summary-bg: #334155;
    }
}

html {
    scroll-behavior: smooth;
    scroll-padding-top: 70px;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.5;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* 焦点可见性（无障碍） */
a:focus-visible,
button:focus-visible,
summary:focus-visible {
    outline: none;
    box-shadow: var(--focus-ring);
    border-radius: 6px;
}

/* 顶部固定导航栏 */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: 60px;
    background: var(--nav-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 20px;
}

.brand-logo {
    display: flex;
    align-items: center;
    gap: 10px;
    text-decoration: none;
    flex-shrink: 0;
}

.logo-icon-wrapper {
    width: 36px;
    height: 36px;
    background: linear-gradient(135deg, #0284c7 0%, #4f46e5 100%);
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: #ffffff;
    font-size: 1.15rem;
    box-shadow: 0 4px 10px rgba(2, 132, 199, 0.25);
}

.brand-title {
    font-size: 1.25rem;
    font-weight: 900;
    letter-spacing: 0.5px;
    background: linear-gradient(135deg, #0284c7, #4f46e5);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.brand-subtitle {
    font-size: 0.6rem;
    color: var(--text-secondary);
    font-weight: 700;
    letter-spacing: 0.8px;
    margin-top: -3px;
}

.nav-right-container {
    display: flex;
    align-items: center;
    gap: 12px;
    overflow: hidden;
}

.nav-menu-wrapper {
    display: flex;
    overflow-x: auto;
    white-space: nowrap;
    scrollbar-width: none;
}

.nav-menu-wrapper::-webkit-scrollbar {
    display: none;
}

.nav-menu {
    display: flex;
    gap: 4px;
    list-style: none;
}

.nav-menu a {
    text-decoration: none;
    color: var(--text-secondary);
    font-size: 0.85rem;
    font-weight: 600;
    padding: 6px 12px;
    border-radius: 16px;
    transition: all 0.2s ease;
}

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

/* 主题切换按钮 */
.theme-toggle-btn {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    width: 36px;
    height: 36px;
    border-radius: 50%;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1rem;
    flex-shrink: 0;
    transition: all 0.2s ease;
}

.theme-toggle-btn:hover {
    background-color: var(--card-hover);
    color: var(--accent-color);
    border-color: var(--accent-color);
}

/* Header 区域 */
header {
    margin-top: 60px;
    text-align: center;
    padding: 40px 15px 25px;
    background: var(--header-bg);
    position: relative;
}

header h1 {
    font-size: 1.7rem;
    color: var(--text-primary);
    margin-bottom: 8px;
    font-weight: 800;
}

header p {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
}

/* 主内容容器 */
.container {
    max-width: 1400px;
    width: 100%;
    margin: 0 auto;
    padding: 0 15px 40px;
    flex: 1 0 auto;
}

/* 模块标题 */
.section-title {
    font-size: 1.25rem;
    margin: 35px 0 16px;
    display: flex;
    align-items: center;
    gap: 10px;
    border-bottom: 2px solid var(--border-color);
    padding-bottom: 8px;
    color: var(--text-primary);
    font-weight: 700;
}

.section-title i {
    color: var(--accent-icon);
}

/* AI 工具网格：自适应最小宽度 140px */
.grid-ai {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
    gap: 10px;
}

/* 标准课程/资源网格：自适应最小宽度 210px */
.grid-cards {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(210px, 1fr));
    gap: 12px;
}

/* AI 工具小卡片样式 */
.ai-card {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 12px 6px;
    text-align: center;
    text-decoration: none;
    color: var(--text-primary);
    box-shadow: var(--shadow-sm);
    transition: all 0.2s ease;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: space-between;
    gap: 6px;
}

.ai-card:hover {
    transform: translateY(-2px);
    border-color: var(--accent-color);
    box-shadow: var(--shadow-hover);
}

.ai-card i {
    font-size: 1.4rem;
    color: var(--accent-icon);
}

.ai-card .ai-name {
    font-size: 0.85rem;
    font-weight: 700;
}

.ai-tag {
    font-size: 0.7rem;
    line-height: 1.2;
    padding: 3px 6px;
    border-radius: 12px;
    font-weight: 600;
    letter-spacing: 0.2px;
    display: inline-block;
    white-space: nowrap;
}

.tag-chat { background-color: var(--tag-chat-bg); color: var(--tag-chat-text); }
.tag-multi { background-color: var(--tag-multi-bg); color: var(--tag-multi-text); }
.tag-media { background-color: var(--tag-media-bg); color: var(--tag-media-text); }

/* 标准卡片样式 */
.card {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 12px;
    text-decoration: none;
    color: var(--text-primary);
    box-shadow: var(--shadow-sm);
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    gap: 10px;
    position: relative;
}

.card:hover:not(.card-disabled) {
    transform: translateY(-2px);
    border-color: var(--accent-color);
    box-shadow: var(--shadow-hover);
}

.card-icon {
    width: 36px;
    height: 36px;
    background: var(--accent-light);
    border-radius: 8px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.1rem;
    color: var(--accent-icon);
    flex-shrink: 0;
}

.card-content {
    overflow: hidden;
    width: 100%;
}

.card-content h3 {
    font-size: 0.88rem;
    font-weight: 700;
    color: var(--text-primary);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.card-content p {
    font-size: 0.75rem;
    color: var(--text-secondary);
    font-weight: 500;
    margin-top: 2px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

/* 未完成卡片的“建设中”样式 */
.card-disabled {
    opacity: 0.75;
    cursor: pointer;
    border-style: dashed;
    background-color: var(--card-bg);
    transition: all 0.2s ease;
}

.card-disabled:hover {
    opacity: 1;
    border-color: #ef4444;
    transform: translateY(-2px);
    box-shadow: var(--shadow-hover);
}

.badge-building {
    font-size: 0.65rem;
    padding: 1px 5px;
    border-radius: 4px;
    background-color: rgba(239, 68, 68, 0.15);
    color: #ef4444;
    border: 1px solid rgba(239, 68, 68, 0.3);
    font-weight: 600;
    margin-left: 4px;
    flex-shrink: 0;
}

/* 动态资讯归档板块 */
.blog-container { display: flex; flex-direction: column; gap: 10px; }

.blog-archive details {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    overflow: hidden;
    box-shadow: var(--shadow-sm);
}

.blog-archive summary {
    padding: 12px 16px;
    font-weight: 700;
    cursor: pointer;
    background-color: var(--summary-bg);
    user-select: none;
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.9rem;
    color: var(--text-primary);
}

.blog-list { list-style: none; }
.blog-item { border-top: 1px solid var(--border-color); }
.blog-item a {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 10px 16px;
    text-decoration: none;
    color: var(--text-primary);
    font-size: 0.85rem;
}

.blog-item a:hover { background-color: var(--card-hover); }
.blog-title { font-weight: 600; padding-right: 10px; }
.blog-date { font-size: 0.75rem; color: var(--text-muted); white-space: nowrap; font-weight: 500; }

/* 页脚区域 */
footer {
    background-color: var(--card-bg);
    border-top: 1px solid var(--border-color);
    padding: 25px 20px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    flex-shrink: 0;
    margin-top: auto;
}

.footer-content {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    align-items: center;
    gap: 15px;
}

.version-badge {
    display: inline-block;
    background-color: var(--accent-light);
    color: var(--accent-icon);
    font-size: 0.7rem;
    font-weight: 700;
    padding: 2px 6px;
    border-radius: 4px;
    margin-left: 6px;
}

.footer-contact {
    display: flex;
    gap: 18px;
    align-items: center;
}

.footer-contact a {
    color: var(--text-secondary);
    text-decoration: none;
    transition: color 0.2s ease;
    display: flex;
    align-items: center;
    gap: 6px;
    font-weight: 600;
}

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

/* 响应式微调 */
@media (max-width: 768px) {
    .brand-subtitle { display: none; }
}

@media (max-width: 480px) {
    .footer-content { flex-direction: column; text-align: center; }
    .footer-contact { justify-content: center; flex-wrap: wrap; }
}