/* ===== 每日算法 · 变量语义法 ===== */
/* 设计系统：深色专业风格 + 高可读性排版 */

:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-card: #1c2128;
    --bg-code: #0d1117;
    --bg-highlight: rgba(88, 166, 255, 0.06);
    --border: #30363d;
    --border-light: #21262d;
    --text-primary: #e6edf3;
    --text-secondary: #8b949e;
    --text-tertiary: #6e7681;
    --text-link: #58a6ff;
    --accent-blue: #58a6ff;
    --accent-green: #3fb950;
    --accent-orange: #d29922;
    --accent-red: #f85149;
    --accent-purple: #a371f7;
    --accent-cyan: #39c5cf;
    --difficulty-easy: #3fb950;
    --difficulty-medium: #d29922;
    --difficulty-hard: #f85149;
    --radius: 8px;
    --radius-lg: 12px;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
    --font-sans: 'Noto Sans SC', 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', 'Cascadia Code', 'SF Mono', monospace;
    --container-width: 880px;
}

/* ===== Reset & Base ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

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

body {
    font-family: var(--font-sans);
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.7;
    min-height: 100vh;
}

.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 0 24px;
}

a { color: var(--text-link); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ===== Header ===== */
.site-header {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    padding: 14px 0;
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(12px);
}

.site-header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    display: flex;
    align-items: center;
    gap: 8px;
    color: var(--text-primary);
    font-weight: 700;
    font-size: 1.1rem;
    text-decoration: none;
}

.logo:hover { text-decoration: none; opacity: 0.85; }

.logo-icon {
    color: var(--accent-blue);
    font-size: 1.3rem;
}

.header-date {
    font-family: var(--font-mono);
    font-size: 0.85rem;
    color: var(--text-tertiary);
}

/* ===== Index Page ===== */
.index-hero {
    text-align: center;
    padding: 64px 0 48px;
}

.index-hero h1 {
    font-size: 2.2rem;
    font-weight: 700;
    margin-bottom: 8px;
    letter-spacing: -0.02em;
}

.index-hero .subtitle {
    color: var(--text-secondary);
    font-size: 1.05rem;
}

.today-problem {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 28px 32px;
    margin-bottom: 40px;
    transition: border-color 0.2s;
}

.today-problem:hover { border-color: var(--accent-blue); }

.today-label {
    font-size: 0.8rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--accent-green);
    margin-bottom: 8px;
}

.today-problem h2 {
    font-size: 1.4rem;
    margin-bottom: 4px;
}

.today-problem h2 a {
    color: var(--text-primary);
    text-decoration: none;
}

.today-problem h2 a:hover { color: var(--accent-blue); }

.today-meta {
    display: flex;
    gap: 10px;
    margin-top: 6px;
}

/* ===== Archive ===== */
.archive-section { margin: 48px 0; }

.archive-section h2 {
    font-size: 1.25rem;
    margin-bottom: 16px;
    color: var(--text-secondary);
}

.archive-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    gap: 12px;
}

.archive-item {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 16px 20px;
    transition: border-color 0.2s, transform 0.15s;
}

.archive-item:hover {
    border-color: var(--accent-blue);
    transform: translateY(-1px);
}

.archive-item a { text-decoration: none; display: block; }

.archive-date {
    font-family: var(--font-mono);
    font-size: 0.78rem;
    color: var(--text-tertiary);
    margin-bottom: 4px;
}

.archive-title {
    font-weight: 600;
    color: var(--text-primary);
    font-size: 0.95rem;
}

.archive-type {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-top: 4px;
}

/* ===== Problem Page ===== */
.problem-card { padding: 32px 0 48px; }

.problem-header {
    margin-bottom: 32px;
    padding-bottom: 24px;
    border-bottom: 1px solid var(--border);
}

.problem-meta {
    display: flex;
    gap: 10px;
    align-items: center;
    flex-wrap: wrap;
    margin-bottom: 12px;
}

.problem-id {
    font-family: var(--font-mono);
    font-size: 0.85rem;
    color: var(--text-secondary);
    background: var(--bg-secondary);
    padding: 3px 10px;
    border-radius: 4px;
}

.problem-title {
    font-size: 1.8rem;
    font-weight: 700;
    letter-spacing: -0.01em;
    margin-bottom: 8px;
}

.problem-link {
    font-size: 0.85rem;
}

/* ===== Tags ===== */
.problem-type {
    font-size: 0.78rem;
    font-weight: 600;
    padding: 3px 10px;
    border-radius: 4px;
}

.tag-prefix-hash { background: var(--bg-highlight); color: var(--accent-purple); border: 1px solid rgba(163, 113, 247, 0.3); }
.tag-sliding-fixed { background: rgba(57, 197, 207, 0.08); color: var(--accent-cyan); border: 1px solid rgba(57, 197, 207, 0.3); }
.tag-sliding-var { background: rgba(57, 197, 207, 0.08); color: var(--accent-cyan); border: 1px solid rgba(57, 197, 207, 0.3); }
.tag-mono-stack { background: rgba(210, 153, 34, 0.08); color: var(--accent-orange); border: 1px solid rgba(210, 153, 34, 0.3); }
.tag-linked-list { background: rgba(63, 185, 80, 0.08); color: var(--accent-green); border: 1px solid rgba(63, 185, 80, 0.3); }
.tag-design { background: rgba(163, 113, 247, 0.08); color: var(--accent-purple); border: 1px solid rgba(163, 113, 247, 0.3); }
.tag-dp { background: rgba(248, 81, 73, 0.08); color: var(--accent-red); border: 1px solid rgba(248, 81, 73, 0.3); }
.tag-tree { background: rgba(63, 185, 80, 0.08); color: var(--accent-green); border: 1px solid rgba(63, 185, 80, 0.3); }
.tag-union-find { background: rgba(210, 153, 34, 0.08); color: var(--accent-orange); border: 1px solid rgba(210, 153, 34, 0.3); }
.tag-grid { background: rgba(57, 197, 207, 0.08); color: var(--accent-cyan); border: 1px solid rgba(57, 197, 207, 0.3); }
.tag-topo { background: rgba(163, 113, 247, 0.08); color: var(--accent-purple); border: 1px solid rgba(163, 113, 247, 0.3); }
.tag-two-pointer { background: rgba(58, 166, 255, 0.08); color: var(--accent-blue); border: 1px solid rgba(58, 166, 255, 0.3); }
.tag-bst { background: rgba(248, 81, 73, 0.08); color: var(--accent-red); border: 1px solid rgba(248, 81, 73, 0.3); }
.tag-hash { background: var(--bg-highlight); color: var(--accent-purple); border: 1px solid rgba(163, 113, 247, 0.3); }
.tag-binary-search { background: rgba(58, 166, 255, 0.08); color: var(--accent-blue); border: 1px solid rgba(58, 166, 255, 0.3); }
.tag-center-expand { background: rgba(63, 185, 80, 0.08); color: var(--accent-green); border: 1px solid rgba(63, 185, 80, 0.3); }
.tag-string-sim { background: rgba(57, 197, 207, 0.08); color: var(--accent-cyan); border: 1px solid rgba(57, 197, 207, 0.3); }
.tag-math-sim { background: rgba(210, 153, 34, 0.08); color: var(--accent-orange); border: 1px solid rgba(210, 153, 34, 0.3); }
.tag-backtrack { background: rgba(163, 113, 247, 0.08); color: var(--accent-purple); border: 1px solid rgba(163, 113, 247, 0.3); }
.tag-stack { background: rgba(210, 153, 34, 0.08); color: var(--accent-orange); border: 1px solid rgba(210, 153, 34, 0.3); }
.tag-heap { background: rgba(248, 81, 73, 0.08); color: var(--accent-red); border: 1px solid rgba(248, 81, 73, 0.3); }
.tag-other { background: var(--bg-secondary); color: var(--text-tertiary); border: 1px solid var(--border); }

.tag-daily { background: rgba(63, 185, 80, 0.1); color: var(--accent-green); border: 1px solid rgba(63, 185, 80, 0.3); }

.problem-difficulty {
    font-size: 0.78rem;
    font-weight: 600;
    padding: 3px 10px;
    border-radius: 4px;
}

.difficulty-easy { background: rgba(63, 185, 80, 0.1); color: var(--difficulty-easy); border: 1px solid rgba(63, 185, 80, 0.25); }
.difficulty-medium { background: rgba(210, 153, 34, 0.1); color: var(--difficulty-medium); border: 1px solid rgba(210, 153, 34, 0.25); }
.difficulty-hard { background: rgba(248, 81, 73, 0.1); color: var(--difficulty-hard); border: 1px solid rgba(248, 81, 73, 0.25); }

/* ===== Sections ===== */
.section {
    margin: 28px 0;
    padding: 0 4px;
}

.section-title {
    font-size: 1.15rem;
    font-weight: 600;
    margin-bottom: 14px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.section-icon { font-size: 1.2rem; }

.highlight-box {
    background: var(--bg-highlight);
    border: 1px solid rgba(88, 166, 255, 0.15);
    border-radius: var(--radius-lg);
    padding: 20px 24px;
    margin: 28px -4px;
}

.problem-description {
    color: var(--text-primary);
    font-size: 1rem;
    line-height: 1.8;
}

/* ===== Examples ===== */
.example-block {
    background: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius);
    padding: 16px;
    margin: 12px 0;
}

.example-block h4 {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: 8px;
    font-weight: 600;
}

.example-input, .example-output {
    font-family: var(--font-mono);
    font-size: 0.88rem;
    line-height: 1.5;
}

.example-input { color: var(--text-secondary); margin-bottom: 4px; }
.example-output { color: var(--accent-green); }
.example-label { color: var(--text-tertiary); font-size: 0.82rem; }

/* ===== Var Semantics ===== */
.semantics-list {
    list-style: none;
    counter-reset: sem;
}

.semantics-item {
    counter-increment: sem;
    padding: 12px 0;
    border-bottom: 1px solid var(--border-light);
    line-height: 1.7;
}

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

.semantics-item::before {
    content: counter(sem) ")";
    color: var(--accent-blue);
    font-weight: 700;
    margin-right: 8px;
    font-family: var(--font-mono);
}

.semantics-item code {
    background: rgba(88, 166, 255, 0.12);
    padding: 1px 6px;
    border-radius: 3px;
    font-family: var(--font-mono);
    font-size: 0.92em;
    color: var(--accent-blue);
}

.var-table {
    width: 100%;
    border-collapse: collapse;
    margin: 12px 0;
}

.var-table th, .var-table td {
    text-align: left;
    padding: 10px 14px;
    border-bottom: 1px solid var(--border-light);
    font-size: 0.9rem;
}

.var-table th {
    color: var(--text-secondary);
    font-weight: 600;
    font-size: 0.8rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.var-table code {
    background: rgba(88, 166, 255, 0.1);
    padding: 1px 6px;
    border-radius: 3px;
    font-family: var(--font-mono);
    font-size: 0.9em;
    color: var(--accent-blue);
}

/* ===== Thinking Steps ===== */
.thinking-step {
    padding: 8px 0 8px 20px;
    border-left: 2px solid var(--border);
    margin: 6px 0;
    font-style: italic;
    color: var(--text-secondary);
}

.thinking-step:first-child { border-left-color: var(--accent-green); }
.thinking-step:last-child { border-left-color: var(--accent-blue); }

/* ===== Code ===== */
.code-tabs {
    display: flex;
    gap: 0;
    margin-bottom: 0;
}

.code-tab {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-bottom: none;
    color: var(--text-secondary);
    padding: 8px 18px;
    font-size: 0.85rem;
    font-family: var(--font-mono);
    cursor: pointer;
    border-radius: var(--radius) var(--radius) 0 0;
    margin-right: -1px;
    transition: background 0.15s, color 0.15s;
}

.code-tab.active {
    background: var(--bg-code);
    color: var(--text-primary);
    border-color: var(--border);
}

.code-tab:hover:not(.active) { color: var(--text-primary); }

.code-panel {
    display: none;
    background: var(--bg-code);
    border: 1px solid var(--border);
    border-radius: 0 var(--radius) var(--radius) var(--radius);
    padding: 20px 24px;
    overflow-x: auto;
}

.code-panel.active { display: block; }

pre {
    margin: 0;
    overflow-x: auto;
}

code {
    font-family: var(--font-mono);
    font-size: 0.88rem;
    line-height: 1.6;
}

.language-python, .language-cpp {
    color: var(--text-primary);
}

/* ===== Code Steps ===== */
.code-step {
    padding: 8px 0 8px 8px;
    font-family: var(--font-mono);
    font-size: 0.88rem;
    color: var(--text-secondary);
    border-left: 2px solid var(--accent-purple);
    margin: 4px 0;
}

.code-step code {
    background: rgba(163, 113, 247, 0.1);
    color: var(--accent-purple);
}

/* ===== Complexity ===== */
.complexity {
    display: flex;
    gap: 18px;
    flex-wrap: wrap;
}

.complexity-item {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 14px 20px;
    display: flex;
    align-items: center;
    gap: 10px;
}

.complexity-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.complexity-value {
    font-family: var(--font-mono);
    font-size: 0.95rem;
    color: var(--accent-green);
    background: transparent;
    padding: 0;
}

/* ===== Pitfalls ===== */
.pitfalls-section {
    background: rgba(248, 81, 73, 0.04);
    border: 1px solid rgba(248, 81, 73, 0.15);
    border-radius: var(--radius-lg);
    padding: 20px 24px;
    margin: 28px -4px;
}

.pitfall-item {
    padding: 6px 0;
    display: flex;
    gap: 8px;
    align-items: flex-start;
}

.pitfall-icon { color: var(--accent-red); flex-shrink: 0; }

.pitfall-item code {
    background: rgba(248, 81, 73, 0.1);
    padding: 1px 6px;
    border-radius: 3px;
    font-family: var(--font-mono);
    font-size: 0.9em;
    color: var(--accent-red);
}

/* ===== Edge Cases ===== */
.edge-case {
    background: var(--bg-secondary);
    border: 1px solid var(--border-light);
    border-radius: var(--radius);
    padding: 12px 16px;
    margin: 8px 0;
}

.edge-case .edge-label {
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--accent-orange);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: 4px;
}

.edge-case code {
    font-family: var(--font-mono);
    font-size: 0.88rem;
    color: var(--text-primary);
    background: transparent;
}

/* ===== Audio Player ===== */
.audio-section {
    background: linear-gradient(135deg, rgba(163, 113, 247, 0.08), rgba(88, 166, 255, 0.08));
    border: 1px solid rgba(163, 113, 247, 0.25);
    border-radius: var(--radius-lg);
    padding: 20px 24px;
    margin-bottom: 8px;
}

.audio-hint {
    color: var(--text-secondary);
    font-size: 0.88rem;
    margin-bottom: 16px;
}

.audio-player-wrap {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.audio-player {
    width: 100%;
    height: 48px;
    border-radius: var(--radius);
    outline: none;
}

.audio-player::-webkit-media-controls-panel {
    background: var(--bg-secondary);
}

.playback-speed {
    display: flex;
    align-items: center;
    gap: 8px;
    flex-wrap: wrap;
}

.speed-label {
    font-size: 0.82rem;
    color: var(--text-tertiary);
    margin-right: 4px;
}

.speed-btn {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    color: var(--text-secondary);
    padding: 6px 14px;
    border-radius: 20px;
    font-size: 0.82rem;
    cursor: pointer;
    transition: all 0.15s ease;
    min-width: 52px;
    min-height: 36px;
}

.speed-btn:hover {
    border-color: var(--accent-purple);
    color: var(--text-primary);
}

.speed-btn.active {
    background: rgba(163, 113, 247, 0.15);
    border-color: var(--accent-purple);
    color: var(--accent-purple);
    font-weight: 600;
}

.today-problem .audio-section {
    margin-top: 16px;
    padding: 16px 20px;
}

.today-problem .audio-player {
    height: 44px;
}

/* ===== Footer ===== */
.site-footer {
    border-top: 1px solid var(--border);
    padding: 24px 0;
    margin-top: 48px;
    text-align: center;
    color: var(--text-tertiary);
    font-size: 0.85rem;
}

.site-footer a { color: var(--text-secondary); }
.footer-meta { margin-top: 4px; font-size: 0.78rem; }

/* ===== Responsive ===== */
@media (max-width: 768px) {
    .container { padding: 0 16px; }
    .problem-title { font-size: 1.4rem; }
    .index-hero h1 { font-size: 1.6rem; }
    .code-panel { padding: 14px 16px; }
    .highlight-box, .pitfalls-section { margin: 24px -4px; padding: 16px 18px; }
    .archive-grid { grid-template-columns: 1fr; }
}

/* ===== Print ===== */
@media print {
    .site-header, .site-footer { display: none; }
    body { background: white; color: black; }
    .problem-card { padding: 0; }
}