:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-card: #1c2128;
    --bg-code: #0d1117;
    --text-primary: #e6edf3;
    --text-secondary: #8b949e;
    --text-muted: #6e7681;
    --border-color: #30363d;
    --accent: #58a6ff;
    --accent-hover: #79c0ff;
    --accent-bg: rgba(56,139,253,0.15);
    --success: #3fb950;
    --warning: #d29922;
    --danger: #f85149;
    --shadow: 0 2px 8px rgba(0,0,0,0.3);
    --radius: 8px;
    --transition: 0.25s ease;
}

[data-theme="light"] {
    --bg-primary: #f6f8fa;
    --bg-secondary: #ffffff;
    --bg-card: #ffffff;
    --bg-code: #f6f8fa;
    --text-primary: #1f2328;
    --text-secondary: #656d76;
    --text-muted: #8b949e;
    --border-color: #d0d7de;
    --accent: #0969da;
    --accent-hover: #0550ae;
    --accent-bg: rgba(9,105,218,0.1);
    --shadow: 0 2px 8px rgba(0,0,0,0.08);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Noto Sans SC', sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    transition: background var(--transition), color var(--transition);
    min-height: 100vh;
}

.header {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    padding: 16px 24px;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow);
}

.header-inner {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 12px;
}

.header-left { display: flex; flex-direction: column; gap: 4px; }

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent);
    letter-spacing: -0.5px;
}

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

.header-right {
    display: flex;
    align-items: center;
    gap: 16px;
}

.stats {
    font-size: 0.85rem;
    color: var(--text-secondary);
    padding: 6px 14px;
    background: var(--accent-bg);
    border-radius: 20px;
    border: 1px solid var(--border-color);
}

.theme-toggle {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    cursor: pointer;
    font-size: 1.2rem;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition);
}

.theme-toggle:hover {
    background: var(--accent-bg);
    border-color: var(--accent);
    transform: rotate(30deg);
}

.toolbar {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    padding: 12px 24px;
}

.toolbar-inner {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
    align-items: center;
}

.filter-group {
    display: flex;
    align-items: center;
    gap: 6px;
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.filter-group label { white-space: nowrap; }

.filter-group select,
.search-input {
    background: var(--bg-card);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 6px 12px;
    font-size: 0.9rem;
    outline: none;
    transition: border-color var(--transition);
}

.filter-group select:focus,
.search-input:focus {
    border-color: var(--accent);
}

.search-input { width: 200px; }

.pagination {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    padding: 10px 24px;
}

.pagination-bottom {
    border-bottom: none;
    border-top: 1px solid var(--border-color);
    margin-top: 20px;
}

.pagination-inner {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    gap: 6px;
    flex-wrap: wrap;
    justify-content: center;
}

.page-btn {
    background: var(--bg-card);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 6px 12px;
    cursor: pointer;
    font-size: 0.85rem;
    transition: all var(--transition);
    white-space: nowrap;
}

.page-btn:hover:not(:disabled) {
    background: var(--accent-bg);
    border-color: var(--accent);
    color: var(--accent);
}

.page-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

.page-btn.active {
    background: var(--accent);
    color: #fff;
    border-color: var(--accent);
}

.page-numbers {
    display: flex;
    gap: 4px;
    flex-wrap: wrap;
    justify-content: center;
}

.page-jump {
    display: flex;
    align-items: center;
    gap: 4px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-left: 8px;
}

.page-jump input {
    width: 56px;
    background: var(--bg-card);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 4px 8px;
    text-align: center;
    font-size: 0.85rem;
    outline: none;
}

.page-jump input:focus { border-color: var(--accent); }

.go-btn {
    background: var(--accent) !important;
    color: #fff !important;
    border-color: var(--accent) !important;
    font-weight: 600;
}

.go-btn:hover { opacity: 0.85; }

.page-info {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-left: 8px;
    white-space: nowrap;
}

.questions-container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 20px 24px;
    min-height: 60vh;
}

.loading {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 80px 0;
    color: var(--text-secondary);
}

.spinner {
    width: 40px;
    height: 40px;
    border: 3px solid var(--border-color);
    border-top-color: var(--accent);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
    margin-bottom: 12px;
}

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

.question-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    margin-bottom: 16px;
    overflow: hidden;
    transition: box-shadow var(--transition), border-color var(--transition);
}

.question-card:hover {
    box-shadow: var(--shadow);
    border-color: var(--accent);
}

.question-header {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 14px 18px;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    flex-wrap: wrap;
}

.question-id {
    font-size: 0.8rem;
    font-weight: 700;
    color: var(--accent);
    background: var(--accent-bg);
    padding: 2px 10px;
    border-radius: 12px;
    white-space: nowrap;
}

.question-title {
    font-size: 1rem;
    font-weight: 600;
    flex: 1;
    min-width: 0;
}

.badge {
    font-size: 0.75rem;
    padding: 2px 10px;
    border-radius: 12px;
    font-weight: 600;
    white-space: nowrap;
}

.badge-category {
    background: rgba(56,139,253,0.12);
    color: #58a6ff;
    border: 1px solid rgba(56,139,253,0.3);
}

.badge-easy {
    background: rgba(63,185,80,0.12);
    color: #3fb950;
    border: 1px solid rgba(63,185,80,0.3);
}

.badge-medium {
    background: rgba(210,153,34,0.12);
    color: #d29922;
    border: 1px solid rgba(210,153,34,0.3);
}

.badge-hard {
    background: rgba(248,81,73,0.12);
    color: #f85149;
    border: 1px solid rgba(248,81,73,0.3);
}

.question-body { padding: 16px 18px; }

.question-desc {
    font-size: 0.95rem;
    color: var(--text-primary);
    margin-bottom: 14px;
    line-height: 1.7;
}

.code-block {
    position: relative;
    margin: 10px 0;
    border-radius: var(--radius);
    overflow: hidden;
    border: 1px solid var(--border-color);
}

.code-label {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 6px 14px;
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--text-secondary);
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
}

.copy-btn {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    border-radius: 4px;
    padding: 2px 8px;
    font-size: 0.75rem;
    cursor: pointer;
    transition: all var(--transition);
}

.copy-btn:hover {
    background: var(--accent-bg);
    color: var(--accent);
    border-color: var(--accent);
}

.code-block pre {
    margin: 0 !important;
    padding: 14px !important;
    background: var(--bg-code) !important;
    font-size: 0.88rem !important;
    line-height: 1.6 !important;
    overflow-x: auto;
}

.code-block code {
    font-family: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace !important;
    font-size: 0.88rem !important;
}

.answer-section {
    margin-top: 12px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    overflow: hidden;
}

.answer-toggle {
    width: 100%;
    background: var(--bg-secondary);
    border: none;
    padding: 10px 18px;
    color: var(--accent);
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 8px;
    transition: background var(--transition);
}

.answer-toggle:hover { background: var(--accent-bg); }

.answer-toggle .arrow {
    transition: transform var(--transition);
    font-size: 0.7rem;
}

.answer-toggle.open .arrow { transform: rotate(90deg); }

.answer-content {
    display: none;
    border-top: 1px solid var(--border-color);
}

.answer-content.show { display: block; }

.footer {
    text-align: center;
    padding: 24px;
    color: var(--text-muted);
    font-size: 0.85rem;
    border-top: 1px solid var(--border-color);
    margin-top: 40px;
    background: var(--bg-secondary);
}

.footer p { margin-bottom: 4px; }

.no-results {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-secondary);
}

.no-results .icon { font-size: 3rem; margin-bottom: 12px; }

@media (max-width: 768px) {
    .header-inner { flex-direction: column; align-items: flex-start; }
    .header-right { width: 100%; justify-content: space-between; }
    .toolbar-inner { flex-direction: column; }
    .filter-group { width: 100%; }
    .filter-group select, .search-input { flex: 1; width: 100%; }
    .pagination-inner { gap: 4px; }
    .page-jump { margin-left: 0; }
    .questions-container { padding: 12px; }
    .question-header { padding: 10px 14px; }
    .question-body { padding: 12px 14px; }
    .logo { font-size: 1.2rem; }
}

@media (max-width: 480px) {
    .stats { display: none; }
    .subtitle { font-size: 0.78rem; }
    .page-numbers { gap: 2px; }
    .page-btn { padding: 4px 8px; font-size: 0.8rem; }
}

[data-theme="light"] .badge-category {
    background: rgba(9,105,218,0.1);
    color: #0969da;
    border-color: rgba(9,105,218,0.3);
}

[data-theme="light"] .badge-easy {
    background: rgba(26,127,55,0.1);
    color: #1a7f37;
    border-color: rgba(26,127,55,0.3);
}

[data-theme="light"] .badge-medium {
    background: rgba(154,103,0,0.1);
    color: #9a6700;
    border-color: rgba(154,103,0,0.3);
}

[data-theme="light"] .badge-hard {
    background: rgba(205,41,44,0.1);
    color: #cf292c;
    border-color: rgba(205,41,44,0.3);
}