/* ===========================
   智答 — Design System
   ========================= */

/* --- CSS Variables --- */
:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-card: #1c2128;
    --bg-card-hover: #242a33;
    --text-primary: #e6edf3;
    --text-secondary: #8b949e;
    --text-muted: #484f58;
    --accent: #7c5cfc;
    --accent-glow: rgba(124, 92, 252, 0.3);
    --success: #3fb950;
    --danger: #f85149;
    --warning: #d29922;
    --border: rgba(255,255,255,0.06);
    --radius: 16px;
    --radius-sm: 10px;
    --font: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
    scroll-behavior: smooth;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: var(--font);
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    overflow-x: hidden;
    line-height: 1.6;
}

/* --- Ambient background --- */
body::before {
    content: '';
    position: fixed;
    top: -40%; left: -20%;
    width: 80vw; height: 80vw;
    background: radial-gradient(circle, rgba(124,92,252,0.08), transparent 60%);
    pointer-events: none;
    z-index: 0;
}

body::after {
    content: '';
    position: fixed;
    bottom: -30%; right: -20%;
    width: 60vw; height: 60vw;
    background: radial-gradient(circle, rgba(88,166,255,0.06), transparent 60%);
    pointer-events: none;
    z-index: 0;
}

/* --- Header --- */
.header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: rgba(13,17,23,0.85);
    backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--border);
    padding: 16px 24px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--accent), #58a6ff);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.5px;
}

.logo-icon { margin-right: 6px; }

.header-right {
    display: flex;
    align-items: center;
    gap: 12px;
}

.streak-badge {
    display: flex;
    align-items: center;
    gap: 6px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    padding: 6px 14px;
    border-radius: 20px;
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.streak-badge .streak-fire { font-size: 1.1rem; }
.streak-count { color: var(--warning); font-weight: 600; }

/* --- Category Tabs --- */
.tabs-wrapper {
    position: sticky;
    top: 65px;
    z-index: 90;
    background: rgba(13,17,23,0.85);
    backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--border);
    overflow-x: auto;
    scrollbar-width: none;
    -ms-overflow-style: none;
}

.tabs-wrapper::-webkit-scrollbar { display: none; }

.tabs {
    display: flex;
    gap: 4px;
    padding: 12px 24px;
    min-width: max-content;
}

.tab {
    padding: 8px 18px;
    border-radius: 20px;
    border: none;
    background: transparent;
    color: var(--text-secondary);
    font-family: var(--font);
    font-size: 0.85rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
    white-space: nowrap;
}

.tab:hover {
    background: var(--bg-card);
    color: var(--text-primary);
}

.tab.active {
    background: var(--accent);
    color: #fff;
    box-shadow: 0 2px 12px var(--accent-glow);
}

/* --- Main Content --- */
.main {
    position: relative;
    z-index: 1;
    max-width: 700px;
    margin: 0 auto;
    padding: 24px 16px 100px;
}

/* --- Stats Bar --- */
.stats-bar {
    display: flex;
    gap: 16px;
    margin-bottom: 24px;
    justify-content: center;
}

.stat {
    text-align: center;
    padding: 12px 20px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    min-width: 90px;
}

.stat-number {
    font-size: 1.4rem;
    font-weight: 700;
    color: var(--accent);
}

.stat-label {
    font-size: 0.75rem;
    color: var(--text-muted);
    margin-top: 2px;
}

/* --- Question Card --- */
.card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    overflow: hidden;
    margin-bottom: 20px;
    transition: var(--transition);
    animation: fadeUp 0.4s ease both;
}

.card:hover {
    border-color: rgba(124,92,252,0.2);
    transform: translateY(-2px);
    box-shadow: 0 8px 30px rgba(0,0,0,0.3);
}

@keyframes fadeUp {
    from { opacity: 0; transform: translateY(20px); }
    to   { opacity: 1; transform: translateY(0); }
}

.card-header {
    padding: 20px 24px 16px;
}

.card-category {
    display: inline-flex;
    align-items: center;
    gap: 4px;
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--accent);
    background: rgba(124,92,252,0.1);
    padding: 4px 12px;
    border-radius: 12px;
    margin-bottom: 12px;
}

.card-question {
    font-size: 1.1rem;
    font-weight: 600;
    line-height: 1.5;
    color: var(--text-primary);
}

.card-scene {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-top: 8px;
    font-style: italic;
}

/* --- Answer Toggle Button --- */
.card-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    width: 100%;
    padding: 14px;
    border: none;
    border-top: 1px solid var(--border);
    background: transparent;
    color: var(--accent);
    font-family: var(--font);
    font-size: 0.9rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
}

.card-toggle:hover {
    background: rgba(124,92,252,0.05);
}

.card-toggle .arrow {
    transition: transform 0.3s ease;
    font-size: 0.8rem;
}

.card.open .card-toggle .arrow {
    transform: rotate(180deg);
}

/* --- Answer Content --- */
.card-answer {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.card.open .card-answer {
    max-height: 2000px;
}

.answer-content {
    padding: 0 24px 24px;
}

.answer-section {
    margin-bottom: 16px;
}

.answer-label {
    display: flex;
    align-items: center;
    gap: 6px;
    font-size: 0.8rem;
    font-weight: 600;
    margin-bottom: 8px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.answer-label.bad { color: var(--danger); }
.answer-label.good { color: var(--success); }
.answer-label.tip { color: var(--warning); }

.answer-text {
    font-size: 0.92rem;
    color: var(--text-secondary);
    line-height: 1.7;
    padding: 12px 16px;
    border-radius: var(--radius-sm);
    border-left: 3px solid;
}

.answer-text.bad-text {
    background: rgba(248,81,73,0.06);
    border-color: var(--danger);
}

.answer-text.good-text {
    background: rgba(63,185,80,0.06);
    border-color: var(--success);
    color: var(--text-primary);
}

.answer-text.tip-text {
    background: rgba(210,153,34,0.06);
    border-color: var(--warning);
    font-size: 0.85rem;
}

.answer-alt {
    margin-top: 8px;
    font-size: 0.85rem;
    color: var(--text-muted);
    padding-left: 16px;
}

.answer-alt strong {
    color: var(--text-secondary);
}

/* --- Card number --- */
.card-number {
    font-size: 0.7rem;
    color: var(--text-muted);
    float: right;
    margin-top: 2px;
}

/* --- Load more --- */
.load-more {
    display: block;
    width: 100%;
    padding: 16px;
    border: 1px dashed var(--border);
    border-radius: var(--radius);
    background: transparent;
    color: var(--text-secondary);
    font-family: var(--font);
    font-size: 0.9rem;
    cursor: pointer;
    transition: var(--transition);
    margin-top: 8px;
}

.load-more:hover {
    border-color: var(--accent);
    color: var(--accent);
    background: rgba(124,92,252,0.05);
}

/* --- Empty state --- */
.empty-state {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-muted);
}

.empty-state .empty-icon { font-size: 3rem; margin-bottom: 16px; }
.empty-state p { font-size: 0.9rem; }

/* --- Footer --- */
.footer {
    text-align: center;
    padding: 40px 20px;
    font-size: 0.8rem;
    color: var(--text-muted);
}

/* --- Responsive --- */
@media (max-width: 600px) {
    .header { padding: 12px 16px; }
    .logo { font-size: 1.2rem; }
    .tabs { padding: 10px 16px; }
    .main { padding: 16px 12px 80px; }
    .card-header { padding: 16px 18px 14px; }
    .card-question { font-size: 1rem; }
    .answer-content { padding: 0 18px 18px; }
    .stats-bar { gap: 8px; }
    .stat { min-width: 70px; padding: 10px 12px; }
    .stat-number { font-size: 1.1rem; }
}