:root {
    --primary: #027DFD;
    --primary-light: #E8F4FD;
    --primary-dark: #0553B1;
    --bg: #F7F8FA;
    --card: #FFFFFF;
    --text: #1A1A2E;
    --text-secondary: #6B7280;
    --border: #E5E7EB;
    --green: #10B981;
    --orange: #F59E0B;
    --purple: #8B5CF6;
    --pink: #EC4899;
    --red: #EF4444;
    --cyan: #06B6D4;
    --code-bg: #1E293B;
    --code-text: #E2E8F0;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.8;
    font-size: 15px;
}

/* Sub-page Header */
.sub-header {
    background: linear-gradient(135deg, #027DFD 0%, #0553B1 100%);
    color: white;
    padding: 40px 20px 60px;
    position: relative;
}
.sub-header.green { background: linear-gradient(135deg, #10B981 0%, #059669 100%); }
.sub-header.orange { background: linear-gradient(135deg, #F59E0B 0%, #D97706 100%); }
.sub-header.purple { background: linear-gradient(135deg, #8B5CF6 0%, #7C3AED 100%); }
.sub-header.pink { background: linear-gradient(135deg, #EC4899 0%, #DB2777 100%); }
.sub-header.red { background: linear-gradient(135deg, #EF4444 0%, #DC2626 100%); }
.sub-header.cyan { background: linear-gradient(135deg, #06B6D4 0%, #0891B2 100%); }
.sub-header.indigo { background: linear-gradient(135deg, #6366F1 0%, #4F46E5 100%); }
.sub-header.amber { background: linear-gradient(135deg, #F59E0B 0%, #B45309 100%); }
.sub-header.teal { background: linear-gradient(135deg, #14B8A6 0%, #0D9488 100%); }

.sub-header::after {
    content: '';
    position: absolute;
    bottom: -24px;
    left: 0; right: 0;
    height: 48px;
    background: var(--bg);
    border-radius: 50% 50% 0 0 / 100% 100% 0 0;
}
.sub-header .back {
    display: inline-flex; align-items: center; gap: 6px;
    color: rgba(255,255,255,0.85);
    text-decoration: none;
    font-size: 0.9rem;
    margin-bottom: 20px;
    transition: color 0.2s;
}
.sub-header .back:hover { color: white; }
.sub-header .icon {
    font-size: 2.5rem;
    margin-bottom: 14px;
}
.sub-header h1 {
    font-size: 2.2rem;
    font-weight: 700;
    margin-bottom: 8px;
}
.sub-header p {
    font-size: 1.05rem;
    opacity: 0.9;
    max-width: 700px;
}

/* Container */
.container {
    max-width: 960px;
    margin: 0 auto;
    padding: 20px 20px 60px;
}

/* Sidebar TOC */
.page-layout {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px 20px 60px;
    display: flex;
    gap: 40px;
}
.page-content { flex: 1; min-width: 0; }
.page-toc {
    width: 220px;
    flex-shrink: 0;
    position: sticky;
    top: 20px;
    align-self: flex-start;
    max-height: calc(100vh - 40px);
    overflow-y: auto;
}
.page-toc h4 {
    font-size: 0.8rem;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--text-secondary);
    margin-bottom: 12px;
}
.page-toc a {
    display: block;
    padding: 6px 0 6px 14px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    text-decoration: none;
    border-left: 2px solid var(--border);
    transition: all 0.2s;
}
.page-toc a:hover,
.page-toc a.active {
    color: var(--primary);
    border-left-color: var(--primary);
}

/* Chapter */
.chapter {
    margin-bottom: 48px;
    scroll-margin-top: 24px;
}
.chapter h2 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 16px;
    padding-bottom: 10px;
    border-bottom: 2px solid var(--border);
    display: flex; align-items: center; gap: 10px;
}
.chapter h3 {
    font-size: 1.15rem;
    font-weight: 600;
    margin: 24px 0 12px;
    color: var(--text);
}
.chapter h4 {
    font-size: 1rem;
    font-weight: 600;
    margin: 18px 0 8px;
    color: var(--text-secondary);
}
.chapter p {
    margin-bottom: 12px;
    color: var(--text-secondary);
}
.chapter ul, .chapter ol {
    margin: 8px 0 16px 20px;
    color: var(--text-secondary);
}
.chapter li { margin-bottom: 6px; }
.chapter strong { color: var(--text); }

/* Code Block */
.code-block {
    background: var(--code-bg);
    color: var(--code-text);
    padding: 20px 24px;
    border-radius: 12px;
    font-family: 'SF Mono', 'Fira Code', 'JetBrains Mono', 'Cascadia Code', Menlo, Consolas, monospace;
    font-size: 0.85rem;
    overflow-x: auto;
    margin: 14px 0 20px;
    line-height: 1.7;
    position: relative;
}
.code-block .label {
    position: absolute;
    top: 8px; right: 12px;
    font-size: 0.7rem;
    color: #64748B;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}
.code-block .kw { color: #C084FC; }
.code-block .type { color: #67E8F9; }
.code-block .str { color: #86EFAC; }
.code-block .num { color: #FCA5A5; }
.code-block .cmt { color: #64748B; font-style: italic; }
.code-block .fn { color: #93C5FD; }
.code-block .ann { color: #FCD34D; }
.code-block .prop { color: #FDA4AF; }

/* Inline code */
code {
    background: #F1F5F9;
    padding: 2px 8px;
    border-radius: 5px;
    font-size: 0.88em;
    font-family: 'SF Mono', 'Fira Code', Menlo, Consolas, monospace;
    color: #C7254E;
}

/* Tip / Note / Warning boxes */
.tip, .note, .warning {
    padding: 16px 20px;
    border-radius: 12px;
    margin: 16px 0;
    font-size: 0.9rem;
}
.tip {
    background: #ECFDF5;
    border-left: 4px solid var(--green);
    color: #065F46;
}
.note {
    background: var(--primary-light);
    border-left: 4px solid var(--primary);
    color: #0553B1;
}
.warning {
    background: #FEF3C7;
    border-left: 4px solid var(--orange);
    color: #92400E;
}

/* Cards */
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 16px;
    margin: 16px 0;
}
.info-card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 14px;
    padding: 22px;
    transition: all 0.2s;
}
.info-card:hover {
    box-shadow: 0 4px 20px rgba(0,0,0,0.06);
}
.info-card h4 {
    font-size: 1rem;
    margin: 0 0 10px;
    color: var(--text);
    display: flex; align-items: center; gap: 8px;
}
.info-card p, .info-card li {
    font-size: 0.88rem;
    color: var(--text-secondary);
}
.info-card ul { margin: 0; padding-left: 18px; }

/* Comparison Table */
.compare-table {
    width: 100%;
    border-collapse: collapse;
    margin: 16px 0;
    font-size: 0.88rem;
    background: var(--card);
    border-radius: 12px;
    overflow: hidden;
    border: 1px solid var(--border);
}
.compare-table th {
    background: #F8FAFC;
    padding: 12px 16px;
    text-align: left;
    font-weight: 600;
    border-bottom: 2px solid var(--border);
}
.compare-table td {
    padding: 10px 16px;
    border-bottom: 1px solid var(--border);
    color: var(--text-secondary);
}
.compare-table tr:last-child td { border-bottom: none; }
.compare-table tr:hover td { background: #F8FAFC; }

/* Practice Box */
.practice {
    background: var(--card);
    border: 2px dashed var(--primary);
    border-radius: 14px;
    padding: 24px;
    margin: 20px 0;
}
.practice h4 {
    color: var(--primary);
    margin: 0 0 10px;
    font-size: 1rem;
}
.practice p, .practice li {
    font-size: 0.9rem;
    color: var(--text-secondary);
}
.practice ol, .practice ul { margin: 8px 0 0 20px; }

/* Navigation between chapters */
.chapter-nav {
    display: flex;
    justify-content: space-between;
    gap: 16px;
    margin-top: 48px;
    padding-top: 24px;
    border-top: 2px solid var(--border);
}
.chapter-nav a {
    display: flex;
    flex-direction: column;
    padding: 16px 20px;
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 12px;
    text-decoration: none;
    transition: all 0.2s;
    min-width: 180px;
}
.chapter-nav a:hover {
    border-color: var(--primary);
    box-shadow: 0 4px 16px rgba(2,125,253,0.1);
}
.chapter-nav a .label {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-bottom: 4px;
}
.chapter-nav a .title {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--primary);
}
.chapter-nav .next { text-align: right; margin-left: auto; }

/* Footer */
.footer {
    background: #1E293B;
    color: #94A3B8;
    padding: 32px 20px;
    text-align: center;
    font-size: 0.85rem;
}
.footer a { color: #60A5FA; text-decoration: none; }

/* Responsive */
@media (max-width: 900px) {
    .page-layout { flex-direction: column; }
    .page-toc {
        width: 100%;
        position: static;
        max-height: none;
        display: flex;
        flex-wrap: wrap;
        gap: 4px;
        padding: 16px;
        background: var(--card);
        border-radius: 12px;
        border: 1px solid var(--border);
    }
    .page-toc h4 { width: 100%; }
    .page-toc a {
        border-left: none;
        padding: 6px 12px;
        background: var(--bg);
        border-radius: 6px;
    }
    .sub-header h1 { font-size: 1.7rem; }
    .chapter-nav { flex-direction: column; }
}
@media (max-width: 640px) {
    .card-grid { grid-template-columns: 1fr; }
    .compare-table { font-size: 0.8rem; }
    .compare-table th, .compare-table td { padding: 8px 10px; }
}