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

:root {
    --color-primary: #4f46e5;
    --color-primary-light: #6366f1;
    --color-primary-dark: #4338ca;
    --color-bg: #f8fafc;
    --color-surface: #ffffff;
    --color-text: #1e293b;
    --color-text-secondary: #64748b;
    --color-border: #e2e8f0;
    --color-shadow: rgba(0, 0, 0, 0.08);
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 20px;
    --transition: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: 'Segoe UI', 'Microsoft YaHei', -apple-system, BlinkMacSystemFont, sans-serif;
    background: var(--color-bg);
    color: var(--color-text);
    line-height: 1.7;
    min-height: 100vh;
}

#app {
    min-height: 100vh;
}

a {
    text-decoration: none;
    color: inherit;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 24px 60px;
}

/* ============================
   顶部导航栏
   ============================ */
.navbar {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(255, 255, 255, 0.85);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--color-border);
    padding: 14px 24px;
}

.navbar-inner {
    max-width: 1100px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 20px;
}

.navbar-brand {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 18px;
    font-weight: 700;
    color: var(--color-primary);
    cursor: pointer;
    white-space: nowrap;
}

.navbar-brand .brand-icon {
    font-size: 22px;
}

.navbar-search {
    flex: 1;
    max-width: 360px;
    position: relative;
}

.navbar-search input {
    width: 100%;
    padding: 9px 14px 9px 38px;
    border: 1.5px solid var(--color-border);
    border-radius: 100px;
    font-size: 14px;
    outline: none;
    transition: border-color var(--transition), box-shadow var(--transition);
    background: var(--color-surface);
    color: var(--color-text);
}

.navbar-search input:focus {
    border-color: var(--color-primary-light);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.12);
}

.navbar-search .search-icon {
    position: absolute;
    left: 12px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--color-text-secondary);
    font-size: 16px;
    pointer-events: none;
}

.navbar-links {
    display: flex;
    gap: 6px;
    list-style: none;
}

.navbar-links a {
    padding: 8px 14px;
    border-radius: 100px;
    font-size: 14px;
    font-weight: 500;
    color: var(--color-text-secondary);
    transition: all var(--transition);
    cursor: pointer;
}

.navbar-links a:hover {
    background: var(--color-primary);
    color: #fff;
}

/* ============================
   首页 Hero
   ============================ */
.hero {
    background: linear-gradient(135deg, #4f46e5 0%, #7c3aed 50%, #9333ea 100%);
    color: #fff;
    padding: 72px 24px 56px;
    text-align: center;
    position: relative;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: -40%;
    right: -10%;
    width: 500px;
    height: 500px;
    background: radial-gradient(circle, rgba(255,255,255,0.1) 0%, transparent 70%);
    border-radius: 50%;
}

.hero::after {
    content: '';
    position: absolute;
    bottom: -30%;
    left: -10%;
    width: 400px;
    height: 400px;
    background: radial-gradient(circle, rgba(255,255,255,0.08) 0%, transparent 70%);
    border-radius: 50%;
}

.hero-content {
    position: relative;
    z-index: 1;
    max-width: 680px;
    margin: 0 auto;
}

.hero-title {
    font-size: 38px;
    font-weight: 800;
    letter-spacing: -0.5px;
    margin-bottom: 12px;
    line-height: 1.25;
}

.hero-subtitle {
    font-size: 17px;
    opacity: 0.9;
    margin-bottom: 32px;
}

.search-box {
    display: flex;
    max-width: 480px;
    margin: 0 auto;
    background: #fff;
    border-radius: 100px;
    overflow: hidden;
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.15);
}

.search-box input {
    flex: 1;
    padding: 14px 20px;
    border: none;
    outline: none;
    font-size: 15px;
    color: var(--color-text);
    background: transparent;
}

.search-box button {
    padding: 0 28px;
    border: none;
    background: var(--color-primary);
    color: #fff;
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    transition: background var(--transition);
}

.search-box button:hover {
    background: var(--color-primary-dark);
}

.search-box-inline {
    display: flex;
    gap: 10px;
    margin-bottom: 24px;
}

.search-box-inline input {
    flex: 1;
    padding: 12px 18px;
    border: 1.5px solid var(--color-border);
    border-radius: var(--radius-md);
    font-size: 15px;
    outline: none;
    transition: border-color var(--transition);
}

.search-box-inline input:focus {
    border-color: var(--color-primary-light);
}

.search-box-inline button {
    padding: 12px 28px;
    border: none;
    background: var(--color-primary);
    color: #fff;
    border-radius: var(--radius-md);
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    transition: background var(--transition);
    white-space: nowrap;
}

.search-box-inline button:hover {
    background: var(--color-primary-dark);
}

/* ============================
   分类卡片网格
   ============================ */
.category-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    gap: 20px;
    margin: 36px 0;
}

.category-card {
    background: var(--color-surface);
    border-radius: var(--radius-lg);
    padding: 28px 24px;
    border: 1px solid var(--color-border);
    border-top: 4px solid var(--color-primary);
    cursor: pointer;
    transition: all var(--transition);
    box-shadow: 0 1px 3px var(--color-shadow);
}

.category-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 12px 28px var(--color-shadow);
}

.category-icon {
    width: 52px;
    height: 52px;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 26px;
    margin-bottom: 16px;
}

.category-name {
    font-size: 20px;
    font-weight: 700;
    margin-bottom: 4px;
    color: var(--color-text);
}

.category-count {
    font-size: 13px;
    color: var(--color-text-secondary);
    margin-bottom: 14px;
}

.category-subjects {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
}

.subject-tag {
    font-size: 12px;
    padding: 4px 10px;
    background: var(--color-bg);
    border-radius: 100px;
    color: var(--color-text-secondary);
    border: 1px solid var(--color-border);
}

/* ============================
   快速访问
   ============================ */
.quick-access {
    margin-top: 12px;
}

.section-title {
    font-size: 22px;
    font-weight: 700;
    margin-bottom: 18px;
    color: var(--color-text);
}

.formula-chips {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.formula-chip {
    padding: 10px 18px;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 100px;
    font-size: 14px;
    font-weight: 500;
    color: var(--color-text);
    cursor: pointer;
    transition: all var(--transition);
}

.formula-chip:hover {
    background: var(--color-primary);
    color: #fff;
    border-color: var(--color-primary);
    transform: translateY(-2px);
}

/* ============================
   页面头部
   ============================ */
.page-header {
    background: var(--color-surface);
    border-bottom: 4px solid var(--color-primary);
    padding: 28px 24px 24px;
}

.back-link {
    display: inline-block;
    font-size: 14px;
    color: var(--color-text-secondary);
    margin-bottom: 14px;
    transition: color var(--transition);
    cursor: pointer;
}

.back-link:hover {
    color: var(--color-primary);
}

.page-title-row {
    display: flex;
    align-items: center;
    gap: 12px;
    flex-wrap: wrap;
    max-width: 1100px;
    margin: 0 auto;
}

.page-icon {
    font-size: 32px;
}

.page-title {
    font-size: 28px;
    font-weight: 800;
    color: var(--color-text);
}

.page-count {
    font-size: 14px;
    color: var(--color-text-secondary);
    background: var(--color-bg);
    padding: 4px 14px;
    border-radius: 100px;
}

.page-badge {
    font-size: 13px;
    font-weight: 600;
    padding: 5px 14px;
    border-radius: 100px;
    margin-left: auto;
}

/* ============================
   学科分区
   ============================ */
.subject-section {
    margin: 32px 0;
}

.subject-title {
    font-size: 20px;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: 16px;
    padding-bottom: 10px;
    border-bottom: 2px solid var(--color-border);
    display: flex;
    align-items: center;
    gap: 8px;
}

.subject-title::before {
    content: '';
    width: 4px;
    height: 20px;
    background: var(--color-primary);
    border-radius: 2px;
}

.formula-list {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 16px;
}

.formula-card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: 20px;
    cursor: pointer;
    transition: all var(--transition);
    box-shadow: 0 1px 2px var(--color-shadow);
}

.formula-card:hover {
    border-color: var(--color-primary-light);
    box-shadow: 0 6px 20px var(--color-shadow);
    transform: translateY(-2px);
}

.formula-card-name {
    font-size: 16px;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: 10px;
}

.formula-card-expr {
    font-family: 'Cambria Math', 'Times New Roman', Georgia, serif;
    font-size: 16px;
    color: var(--color-primary);
    background: var(--color-bg);
    padding: 10px 14px;
    border-radius: var(--radius-sm);
    margin-bottom: 10px;
    line-height: 1.6;
    word-break: break-word;
}

.formula-card-desc {
    font-size: 13px;
    color: var(--color-text-secondary);
    line-height: 1.5;
}

/* ============================
   公式详情页
   ============================ */
.formula-detail {
    max-width: 820px;
    margin: 0 auto;
    padding: 32px 0;
}

.formula-display {
    background: linear-gradient(135deg, #4f46e5 0%, #6366f1 100%);
    border-radius: var(--radius-lg);
    padding: 36px 32px;
    text-align: center;
    margin-bottom: 32px;
    color: #fff;
    box-shadow: 0 10px 36px rgba(79, 70, 229, 0.22);
}

.formula-display-label {
    font-size: 13px;
    text-transform: uppercase;
    letter-spacing: 2px;
    opacity: 0.7;
    margin-bottom: 14px;
}

.formula-display-expr {
    font-family: 'Cambria Math', 'Times New Roman', Georgia, serif;
    font-size: 24px;
    font-weight: 600;
    line-height: 1.8;
    word-break: break-word;
}

.detail-block {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: 24px 28px;
    margin-bottom: 20px;
    box-shadow: 0 1px 3px var(--color-shadow);
}

.detail-heading {
    font-size: 18px;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: 14px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.detail-heading::before {
    content: '';
    width: 4px;
    height: 18px;
    background: var(--color-primary);
    border-radius: 2px;
    flex-shrink: 0;
}

.detail-text {
    font-size: 15px;
    color: var(--color-text-secondary);
    line-height: 1.85;
}

.source-text {
    font-style: italic;
}

.proof-block {
    border-left: 4px solid var(--color-primary-light);
}

.proof-content {
    font-size: 15px;
    color: var(--color-text);
    line-height: 1.9;
    font-family: 'Cambria Math', 'Times New Roman', Georgia, serif;
    white-space: pre-wrap;
    word-break: break-word;
}

/* 变量表 */
.variable-table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 4px;
}

.variable-table th {
    text-align: left;
    padding: 10px 14px;
    background: var(--color-bg);
    font-size: 14px;
    font-weight: 600;
    color: var(--color-text-secondary);
    border-bottom: 2px solid var(--color-border);
}

.variable-table td {
    padding: 12px 14px;
    font-size: 14px;
    border-bottom: 1px solid var(--color-border);
}

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

.var-symbol {
    font-family: 'Cambria Math', 'Times New Roman', Georgia, serif;
    font-weight: 700;
    color: var(--color-primary);
    white-space: nowrap;
    width: 120px;
}

/* 示例 */
.example-list {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.example-item {
    background: var(--color-bg);
    border-radius: var(--radius-sm);
    padding: 14px 18px;
    font-size: 14px;
    line-height: 1.7;
    color: var(--color-text);
    border-left: 3px solid var(--color-primary-light);
}

/* 相关公式 */
.related-formulas {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.related-chip {
    padding: 8px 16px;
    background: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: 100px;
    font-size: 14px;
    color: var(--color-text);
    cursor: pointer;
    transition: all var(--transition);
}

.related-chip:hover {
    background: var(--color-primary);
    color: #fff;
    border-color: var(--color-primary);
}

/* ============================
   搜索结果
   ============================ */
.search-results {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 16px;
    margin-top: 20px;
}

.search-result-card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: 20px;
    cursor: pointer;
    transition: all var(--transition);
    box-shadow: 0 1px 2px var(--color-shadow);
}

.search-result-card:hover {
    border-color: var(--color-primary-light);
    box-shadow: 0 6px 20px var(--color-shadow);
    transform: translateY(-2px);
}

.search-result-cat {
    font-size: 12px;
    font-weight: 600;
    margin-bottom: 8px;
}

.search-result-name {
    font-size: 16px;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: 8px;
}

.search-result-expr {
    font-family: 'Cambria Math', 'Times New Roman', Georgia, serif;
    font-size: 15px;
    color: var(--color-primary);
    background: var(--color-bg);
    padding: 8px 12px;
    border-radius: var(--radius-sm);
    margin-bottom: 8px;
    word-break: break-word;
}

.search-result-desc {
    font-size: 13px;
    color: var(--color-text-secondary);
    line-height: 1.5;
}

/* ============================
   空状态
   ============================ */
.empty-state {
    text-align: center;
    padding: 80px 24px;
}

.empty-state h2 {
    font-size: 48px;
    color: var(--color-text-secondary);
    margin-bottom: 12px;
}

.empty-state p {
    font-size: 16px;
    color: var(--color-text-secondary);
    margin-bottom: 20px;
}

/* ============================
   页脚
   ============================ */
.footer {
    text-align: center;
    padding: 32px 24px;
    color: var(--color-text-secondary);
    font-size: 14px;
    border-top: 1px solid var(--color-border);
    background: var(--color-surface);
}

.footer a {
    color: var(--color-primary);
    font-weight: 500;
    cursor: pointer;
}

/* ============================
   响应式适配
   ============================ */
@media (max-width: 768px) {
    .hero-title {
        font-size: 28px;
    }

    .hero-subtitle {
        font-size: 15px;
    }

    .search-box {
        flex-direction: row;
    }

    .search-box button {
        padding: 0 18px;
    }

    .navbar-search {
        display: none;
    }

    .navbar-links {
        display: none;
    }

    .page-title {
        font-size: 22px;
    }

    .formula-display-expr {
        font-size: 18px;
    }

    .formula-display {
        padding: 24px 20px;
    }

    .detail-block {
        padding: 20px 18px;
    }

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

    .formula-list {
        grid-template-columns: 1fr;
    }

    .search-results {
        grid-template-columns: 1fr;
    }

    .page-badge {
        margin-left: 0;
    }

    .var-symbol {
        width: 80px;
    }
}

@media (max-width: 480px) {
    .hero {
        padding: 48px 16px 40px;
    }

    .hero-title {
        font-size: 24px;
    }

    .container {
        padding: 0 16px 40px;
    }

    .formula-display-expr {
        font-size: 16px;
    }
}

/* 滚动条美化 */
::-webkit-scrollbar {
    width: 10px;
}

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

::-webkit-scrollbar-thumb {
    background: #cbd5e1;
    border-radius: 5px;
}

::-webkit-scrollbar-thumb:hover {
    background: #94a3b8;
}

/* 选中文字颜色 */
::selection {
    background: rgba(79, 70, 229, 0.2);
    color: var(--color-text);
}