/* ============================================================
 * 学习系统 — Apple Design 公共设计系统
 * 基于 WWDC Designing Fluid Interfaces (2018)
 * 所有页面共享此文件
 * ============================================================ */

/* --- 1. CSS Reset & 基础 --- */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    text-rendering: optimizeLegibility;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Helvetica Neue", "PingFang SC", "Microsoft YaHei", sans-serif;
    color: var(--text-primary);
    background: var(--bg);
    line-height: 1.47059;
    letter-spacing: -0.022em;
    overflow-x: hidden;
}

/* --- 2. Apple 色彩系统 --- */
:root {
    /* 背景 */
    --bg: #ffffff;
    --bg-secondary: #f5f5f7;
    --bg-tertiary: #ffffff;
    
    /* 表面/卡片 */
    --surface: #ffffff;
    --surface-hover: #f5f5f7;
    --surface-active: #e8e8ed;
    
    /* 文字 */
    --text-primary: #1d1d1f;
    --text-secondary: #6e6e73;
    --text-tertiary: #86868b;
    --text-inverse: #ffffff;
    
    /* 品牌色 */
    --blue: #0071e3;
    --blue-hover: #0077ed;
    --blue-active: #006edb;
    --blue-light: rgba(0, 113, 227, 0.08);
    
    /* 语义色 */
    --green: #34c759;
    --green-light: rgba(52, 199, 89, 0.1);
    --orange: #ff9500;
    --orange-light: rgba(255, 149, 0, 0.1);
    --red: #ff3b30;
    --red-light: rgba(255, 59, 48, 0.1);
    --purple: #af52de;
    --purple-light: rgba(175, 82, 222, 0.1);
    --teal: #5ac8fa;
    --teal-light: rgba(90, 200, 250, 0.1);
    
    /* 边框 */
    --border: rgba(0, 0, 0, 0.08);
    --border-strong: rgba(0, 0, 0, 0.16);
    
    /* 阴影 */
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.04), 0 1px 2px rgba(0, 0, 0, 0.06);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.05), 0 2px 4px -1px rgba(0, 0, 0, 0.04);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.06), 0 4px 10px rgba(0, 0, 0, 0.04);
    --shadow-xl: 0 20px 50px rgba(0, 0, 0, 0.08), 0 8px 20px rgba(0, 0, 0, 0.04);
    
    /* 圆角 */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 20px;
    --radius-full: 980px;
    
    /* 间距 */
    --space-xs: 4px;
    --space-sm: 8px;
    --space-md: 16px;
    --space-lg: 24px;
    --space-xl: 32px;
    --space-2xl: 48px;
    
    /* 动画 — Apple Spring */
    --ease-default: cubic-bezier(0.25, 0.1, 0.25, 1);
    --ease-spring: cubic-bezier(0.175, 0.885, 0.32, 1.275);
    --duration-fast: 150ms;
    --duration-normal: 250ms;
    --duration-slow: 400ms;
}

/* --- 3. Typography — Apple 排版系统 --- */
.heading-hero {
    font-size: 48px;
    font-weight: 700;
    letter-spacing: -0.032em;
    line-height: 1.08349;
}

.heading-large {
    font-size: 32px;
    font-weight: 700;
    letter-spacing: -0.024em;
    line-height: 1.125;
}

.heading-medium {
    font-size: 24px;
    font-weight: 600;
    letter-spacing: -0.022em;
    line-height: 1.16667;
}

.heading-small {
    font-size: 20px;
    font-weight: 600;
    letter-spacing: -0.017em;
    line-height: 1.2;
}

.text-body {
    font-size: 17px;
    font-weight: 400;
    line-height: 1.47059;
    letter-spacing: -0.022em;
}

.text-callout {
    font-size: 15px;
    font-weight: 400;
    line-height: 1.33337;
    letter-spacing: -0.016em;
}

.text-caption {
    font-size: 13px;
    font-weight: 400;
    line-height: 1.38462;
    letter-spacing: -0.01em;
    color: var(--text-secondary);
}

/* --- 4. 容器布局 --- */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--space-lg);
}

.page-header {
    padding: var(--space-2xl) 0 var(--space-lg);
}

.page-header h1 {
    font-size: 32px;
    font-weight: 700;
    letter-spacing: -0.024em;
    line-height: 1.125;
    color: var(--text-primary);
}

.page-header .subtitle {
    font-size: 17px;
    color: var(--text-secondary);
    margin-top: var(--space-xs);
    letter-spacing: -0.022em;
}

/* --- 5. 导航栏 --- */
.navbar {
    position: sticky;
    top: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.72);
    backdrop-filter: saturate(180%) blur(20px);
    -webkit-backdrop-filter: saturate(180%) blur(20px);
    border-bottom: 0.5px solid var(--border);
    padding: 0 var(--space-lg);
    height: 52px;
}

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

.navbar-brand {
    font-size: 17px;
    font-weight: 600;
    color: var(--text-primary);
    text-decoration: none;
    letter-spacing: -0.022em;
}

.navbar-menu {
    display: flex;
    gap: var(--space-xs);
}

.navbar-link {
    font-size: 13px;
    font-weight: 400;
    color: var(--text-secondary);
    text-decoration: none;
    padding: 6px 12px;
    border-radius: var(--radius-full);
    transition: all var(--duration-fast) var(--ease-default);
    letter-spacing: -0.01em;
}

.navbar-link:hover {
    color: var(--text-primary);
    background: var(--surface-hover);
}

.navbar-link.active {
    color: var(--blue);
    background: var(--blue-light);
}

.navbar-user {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

.user-avatar {
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--blue) 0%, var(--purple) 100%);
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-inverse);
    font-weight: 600;
    font-size: 13px;
}

.user-name {
    font-size: 13px;
    color: var(--text-primary);
}

.btn-logout {
    background: var(--surface-hover);
    border: none;
    padding: 6px 16px;
    border-radius: var(--radius-full);
    font-size: 13px;
    color: var(--text-secondary);
    cursor: pointer;
    font-family: inherit;
    transition: all var(--duration-fast) var(--ease-default);
}

.btn-logout:hover {
    background: var(--surface-active);
    color: var(--text-primary);
}

.btn-logout:active {
    transform: scale(0.97);
}

/* 二级导航 */
.sub-navbar {
    position: sticky;
    top: 52px;
    z-index: 999;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: saturate(180%) blur(20px);
    -webkit-backdrop-filter: saturate(180%) blur(20px);
    border-bottom: 0.5px solid var(--border);
    padding: 0 var(--space-lg);
    height: 40px;
}

.sub-navbar-content {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    gap: var(--space-xs);
    height: 100%;
}

/* 管理员入口按钮 */
.admin-link {
    font-size: 12px !important;
    background: var(--blue) !important;
    color: var(--text-inverse) !important;
    border-radius: var(--radius-full) !important;
    padding: 4px 12px !important;
    text-decoration: none;
    cursor: pointer;
    transition: all var(--duration-fast) var(--ease-default);
}

.admin-link:hover {
    background: var(--blue-hover) !important;
    color: var(--text-inverse) !important;
}

/* --- 6. 卡片 --- */
.card {
    background: var(--surface);
    border-radius: var(--radius-lg);
    border: 0.5px solid var(--border);
    box-shadow: var(--shadow-sm);
    padding: var(--space-lg);
    transition: all var(--duration-normal) var(--ease-default);
}

.card:hover {
    box-shadow: var(--shadow-md);
    border-color: var(--border-strong);
}

.card-clickable {
    cursor: pointer;
}

.card-clickable:active {
    transform: scale(0.98);
    transition: transform var(--duration-fast) var(--ease-default);
}

.card-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: var(--space-md);
}

.card-title {
    font-size: 17px;
    font-weight: 600;
    letter-spacing: -0.022em;
    color: var(--text-primary);
}

.card-body {
    color: var(--text-secondary);
    font-size: 15px;
    line-height: 1.47;
}

/* 网格卡片布局 */
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: var(--space-md);
}

/* 统计卡片 */
.stat-card {
    background: var(--surface);
    border-radius: var(--radius-lg);
    border: 0.5px solid var(--border);
    padding: var(--space-lg);
    text-align: center;
}

.stat-card .stat-value {
    font-size: 40px;
    font-weight: 700;
    letter-spacing: -0.032em;
    color: var(--text-primary);
    line-height: 1.1;
}

.stat-card .stat-label {
    font-size: 13px;
    color: var(--text-secondary);
    margin-top: var(--space-xs);
    letter-spacing: -0.01em;
}

.stat-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
    gap: var(--space-md);
}

/* --- 7. 按钮 --- */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-sm);
    font-family: inherit;
    font-size: 15px;
    font-weight: 500;
    letter-spacing: -0.016em;
    line-height: 1;
    padding: 10px 20px;
    border-radius: var(--radius-full);
    border: none;
    cursor: pointer;
    text-decoration: none;
    transition: all var(--duration-fast) var(--ease-default);
    white-space: nowrap;
    user-select: none;
    -webkit-user-select: none;
}

.btn:active {
    transform: scale(0.97);
}

.btn-primary {
    background: var(--blue);
    color: var(--text-inverse);
}

.btn-primary:hover {
    background: var(--blue-hover);
}

.btn-secondary {
    background: var(--surface-hover);
    color: var(--text-primary);
}

.btn-secondary:hover {
    background: var(--surface-active);
}

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

.btn-ghost:hover {
    background: var(--blue-light);
}

.btn-danger {
    background: var(--red);
    color: var(--text-inverse);
}

.btn-sm {
    font-size: 13px;
    padding: 6px 14px;
}

.btn-lg {
    font-size: 17px;
    padding: 14px 28px;
}

/* --- 8. 表单 --- */
.form-group {
    margin-bottom: var(--space-md);
}

.form-label {
    display: block;
    font-size: 13px;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: var(--space-xs);
    letter-spacing: -0.01em;
}

.form-input,
.form-select,
.form-textarea {
    width: 100%;
    font-family: inherit;
    font-size: 17px;
    letter-spacing: -0.022em;
    color: var(--text-primary);
    background: var(--surface);
    border: 1px solid var(--border-strong);
    border-radius: var(--radius-md);
    padding: 10px 14px;
    outline: none;
    transition: all var(--duration-fast) var(--ease-default);
}

.form-input:focus,
.form-select:focus,
.form-textarea:focus {
    border-color: var(--blue);
    box-shadow: 0 0 0 4px rgba(0, 113, 227, 0.15);
}

.form-input::placeholder {
    color: var(--text-tertiary);
}

.form-textarea {
    min-height: 100px;
    resize: vertical;
    line-height: 1.47;
}

/* --- 9. 标签 --- */
.tag {
    display: inline-flex;
    align-items: center;
    font-size: 12px;
    font-weight: 500;
    padding: 3px 10px;
    border-radius: var(--radius-full);
    letter-spacing: -0.006em;
}

.tag-blue { background: var(--blue-light); color: var(--blue); }
.tag-green { background: var(--green-light); color: var(--green); }
.tag-orange { background: var(--orange-light); color: var(--orange); }
.tag-red { background: var(--red-light); color: var(--red); }
.tag-purple { background: var(--purple-light); color: var(--purple); }
.tag-teal { background: var(--teal-light); color: var(--teal); }

/* --- 10. 表格 --- */
.table-container {
    background: var(--surface);
    border-radius: var(--radius-lg);
    border: 0.5px solid var(--border);
    overflow: hidden;
}

.table {
    width: 100%;
    border-collapse: collapse;
    font-size: 15px;
}

.table th {
    font-size: 12px;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.02em;
    text-align: left;
    padding: 12px var(--space-md);
    background: var(--bg-secondary);
    border-bottom: 0.5px solid var(--border);
}

.table td {
    padding: 14px var(--space-md);
    border-bottom: 0.5px solid var(--border);
    color: var(--text-primary);
    letter-spacing: -0.016em;
}

.table tbody tr {
    transition: background var(--duration-fast) var(--ease-default);
}

.table tbody tr:hover {
    background: var(--bg-secondary);
}

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

/* --- 11. 进度条 --- */
.progress-bar {
    width: 100%;
    height: 6px;
    background: var(--bg-secondary);
    border-radius: 3px;
    overflow: hidden;
}

.progress-bar-fill {
    height: 100%;
    border-radius: 3px;
    background: var(--blue);
    transition: width var(--duration-slow) var(--ease-spring);
}

.progress-bar-fill.green { background: var(--green); }
.progress-bar-fill.orange { background: var(--orange); }
.progress-bar-fill.red { background: var(--red); }

/* --- 12. 空状态 --- */
.empty-state {
    text-align: center;
    padding: var(--space-2xl) var(--space-lg);
}

.empty-state-icon {
    font-size: 48px;
    margin-bottom: var(--space-md);
}

.empty-state-title {
    font-size: 20px;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-xs);
    letter-spacing: -0.017em;
}

.empty-state-desc {
    font-size: 15px;
    color: var(--text-secondary);
    margin-bottom: var(--space-lg);
}

/* --- 13. 模态框/遮罩 --- */
.modal-overlay {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.4);
    backdrop-filter: blur(4px);
    -webkit-backdrop-filter: blur(4px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 2000;
    opacity: 0;
    visibility: hidden;
    transition: all var(--duration-normal) var(--ease-default);
}

.modal-overlay.active {
    opacity: 1;
    visibility: visible;
}

.modal {
    background: var(--surface);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-xl);
    width: 90%;
    max-width: 520px;
    max-height: 85vh;
    overflow-y: auto;
    padding: var(--space-xl);
    transform: scale(0.95) translateY(10px);
    transition: transform var(--duration-normal) var(--ease-spring);
}

.modal-overlay.active .modal {
    transform: scale(1) translateY(0);
}

.modal-title {
    font-size: 20px;
    font-weight: 600;
    letter-spacing: -0.017em;
    margin-bottom: var(--space-lg);
}

.modal-actions {
    display: flex;
    gap: var(--space-sm);
    justify-content: flex-end;
    margin-top: var(--space-xl);
}

/* --- 14. Toast/提示 --- */
.toast {
    position: fixed;
    top: 64px;
    right: var(--space-lg);
    background: var(--text-primary);
    color: var(--text-inverse);
    padding: 12px 20px;
    border-radius: var(--radius-md);
    font-size: 15px;
    font-weight: 500;
    box-shadow: var(--shadow-lg);
    transform: translateX(120%);
    transition: transform var(--duration-normal) var(--ease-spring);
    z-index: 3000;
    letter-spacing: -0.016em;
}

.toast.show {
    transform: translateX(0);
}

.toast.toast-success {
    background: var(--green);
    color: white;
}

.toast.toast-error {
    background: var(--red);
    color: white;
}

/* --- 15. 页面特定：登录页 --- */
.login-container {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--bg-secondary);
    padding: var(--space-lg);
}

.login-card {
    background: var(--surface);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-lg);
    padding: var(--space-2xl);
    width: 100%;
    max-width: 420px;
}

/* --- 16. 工具类 --- */
.flex { display: flex; }
.flex-col { flex-direction: column; }
.items-center { align-items: center; }
.justify-between { justify-content: space-between; }
.justify-center { justify-content: center; }
.gap-sm { gap: var(--space-sm); }
.gap-md { gap: var(--space-md); }
.gap-lg { gap: var(--space-lg); }
.text-center { text-align: center; }
.text-right { text-align: right; }
.w-full { width: 100%; }
.mt-sm { margin-top: var(--space-sm); }
.mt-md { margin-top: var(--space-md); }
.mt-lg { margin-top: var(--space-lg); }
.mb-sm { margin-bottom: var(--space-sm); }
.mb-md { margin-bottom: var(--space-md); }
.mb-lg { margin-bottom: var(--space-lg); }
.hidden { display: none !important; }

/* --- 17. 减弱动效 --- */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* --- 18. 响应式 --- */
@media (max-width: 768px) {
    .container {
        padding: 0 var(--space-md);
    }
    
    .card-grid {
        grid-template-columns: 1fr;
    }
    
    .stat-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .page-header h1 {
        font-size: 24px;
    }
    
    .heading-hero {
        font-size: 32px;
    }
    
    .navbar {
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
    }
    
    .navbar-menu {
        flex-wrap: nowrap;
        gap: 2px;
    }
    
    .navbar-link {
        font-size: 12px;
        padding: 6px 8px;
    }
}

@media (max-width: 480px) {
    .stat-grid {
        grid-template-columns: 1fr;
    }
    
    .modal {
        width: 95%;
        padding: var(--space-lg);
    }
}

/* --- 19. Loading 动画 --- */
@keyframes apple-spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

.loading-spinner {
    width: 24px;
    height: 24px;
    border: 3px solid var(--border);
    border-top-color: var(--blue);
    border-radius: 50%;
    animation: apple-spin 0.8s linear infinite;
}

.loading-page {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 50vh;
    gap: var(--space-md);
    color: var(--text-secondary);
    font-size: 15px;
}

/* --- 20. 淡入动画 --- */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(12px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeInUp var(--duration-normal) var(--ease-default) both;
}

.fade-in-delay-1 { animation-delay: 50ms; }
.fade-in-delay-2 { animation-delay: 100ms; }
.fade-in-delay-3 { animation-delay: 150ms; }

/* ────────────────────────────────────────────────
   21. 增强响应式（表格/表单/弹窗/按钮 移动端适配）
   P-2 补充，覆盖管理页表格在窄屏的可用性
   ──────────────────────────────────────────────── */

/* 通用表格横向滚动容器（窄屏时允许左右滑动，避免内容挤变形） */
@media (max-width: 768px) {
    .table-container,
    .table-card,
    .m-table {
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
    }

    /* 管理页操作按钮列在窄屏收紧 */
    .table-container table,
    .table-card table,
    .m-table table {
        min-width: 560px; /* 触发横向滚动，避免列挤压 */
    }

    .actions {
        white-space: nowrap;
    }

    /* 工具栏/筛选项堆叠 */
    .filter-bar,
    .toolbar {
        flex-direction: column;
        align-items: stretch;
        gap: var(--space-sm);
    }

    .filter-input,
    .filter-select {
        min-width: 100%;
    }

    /* 按钮换行，避免溢出 */
    .btn-group {
        flex-wrap: wrap;
    }

    /* 分段控件横向滚动 */
    .segmented,
    .tab-bar {
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
        flex-wrap: nowrap;
    }

    /* 弹窗贴边显示 */
    .modal-content {
        width: 94%;
        max-height: 88vh;
        overflow-y: auto;
    }
}

/* 更小屏（<480px）：更激进的收紧 */
@media (max-width: 480px) {
    body { font-size: 15px; }

    .page-header {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--space-sm);
    }

    .btn { padding: 8px 16px; font-size: 13px; }

    .card { padding: var(--space-md); }

    .hero-title,
    .heading-hero { font-size: 26px; }
}

/* ============================================================
 * 21. Dark Mode — 跟随系统偏好
 * 所有使用 var(--xxx) 的页面自动适配，无需修改 HTML
 * ============================================================ */
@media (prefers-color-scheme: dark) {
    :root {
        /* 背景 */
        --bg: #000000;
        --bg-secondary: #1c1c1e;
        --bg-tertiary: #2c2c2e;

        /* 表面/卡片 */
        --surface: #1c1c1e;
        --surface-hover: #2c2c2e;
        --surface-active: #3a3a3c;

        /* 文字 */
        --text-primary: #f5f5f7;
        --text-secondary: #98989d;
        --text-tertiary: #6e6e73;
        --text-inverse: #000000;

        /* 品牌色（暗色模式下略微提亮） */
        --blue: #0a84ff;
        --blue-hover: #409cff;
        --green: #30d158;
        --orange: #ff9f0a;
        --red: #ff453a;
        --purple: #bf5af2;
        --teal: #64d2ff;

        /* 边框与分割线 */
        --border: rgba(255,255,255,0.1);
        --separator: rgba(255,255,255,0.08);

        /* 阴影（暗色模式增强） */
        --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
        --shadow-md: 0 4px 12px rgba(0,0,0,0.4);
        --shadow-lg: 0 8px 30px rgba(0,0,0,0.5);
        --shadow-xl: 0 20px 60px rgba(0,0,0,0.6);
    }
}

/* ============================================================
 * 22. 骨架屏加载组件
 * 用法: <div class="skeleton" style="width:200px;height:20px"></div>
 * ============================================================ */
.skeleton {
    background: linear-gradient(
        90deg,
        var(--surface-hover, #e8e8ed) 25%,
        var(--surface, #f5f5f7) 50%,
        var(--surface-hover, #e8e8ed) 75%
    );
    background-size: 200% 100%;
    animation: skeleton-shimmer 1.5s ease-in-out infinite;
    border-radius: var(--radius-sm, 8px);
    min-height: 16px;
}

@keyframes skeleton-shimmer {
    0% { background-position: 200% 0; }
    100% { background-position: -200% 0; }
}

.skeleton-circle {
    border-radius: 50%;
}

.skeleton-text {
    height: 14px;
    margin-bottom: 8px;
}

.skeleton-text:last-child {
    width: 60%;
}

/* ============================================================
 * 23. 空状态组件
 * 用法: <div class="empty-state"><div class="empty-icon">📭</div>
 *        <h3 class="empty-title">暂无数据</h3>
 *        <p class="empty-desc">描述文字</p></div>
 * ============================================================ */
.empty-state {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: var(--space-2xl, 48px) var(--space-lg, 24px);
    text-align: center;
    animation: fadeInUp 0.4s ease both;
}

.empty-icon {
    font-size: 48px;
    margin-bottom: var(--space-md, 16px);
    opacity: 0.8;
}

.empty-title {
    font-size: 20px;
    font-weight: 600;
    color: var(--text-primary, #1d1d1f);
    margin-bottom: var(--space-xs, 4px);
    letter-spacing: -0.017em;
}

.empty-desc {
    font-size: 15px;
    color: var(--text-secondary, #6e6e73);
    line-height: 1.6;
    max-width: 360px;
}

/* ============================================================
 * 24. Loading 遮罩组件
 * 用法: <div class="loading-overlay"><div class="loading-spinner"></div></div>
 * ============================================================ */
.loading-overlay {
    position: fixed;
    inset: 0;
    background: rgba(255,255,255,0.72);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
}

@media (prefers-color-scheme: dark) {
    .loading-overlay {
        background: rgba(0,0,0,0.6);
    }
    .skeleton {
        background: linear-gradient(
            90deg,
            #2c2c2e 25%,
            #3a3a3c 50%,
            #2c2c2e 75%
        );
        background-size: 200% 100%;
    }
}

.loading-spinner {
    width: 32px;
    height: 32px;
    border: 3px solid var(--border, rgba(0,0,0,0.1));
    border-top-color: var(--blue, #0071e3);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}