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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif;
    background: #f8f9fa;
    color: #333;
    line-height: 1.6;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 0 16px;
}

/* Header */
.header {
    padding: 20px 0;
    border-bottom: 1px solid #eee;
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 24px;
}

.header h1 { font-size: 20px; font-weight: 600; }
.header h1 a { color: inherit; text-decoration: none; }
.header .nav { display: flex; gap: 16px; font-size: 14px; }
.header .nav a {
    color: #666;
    text-decoration: none;
    padding-bottom: 2px;
}
.header .nav a.active {
    color: #2563eb;
    border-bottom: 2px solid #2563eb;
}
.header .nav .github-link {
    color: #666;
    display: flex;
    align-items: center;
    gap: 6px;
    transition: color 0.15s;
}
.header .nav .github-link:hover { color: #333; }
.github-stars {
    font-size: 12px;
    color: #888;
    font-weight: 500;
}
.github-stars:empty { display: none; }

/* Buttons */
.btn {
    padding: 10px 24px;
    border-radius: 6px;
    font-size: 14px;
    font-weight: 500;
    cursor: pointer;
    border: none;
    transition: opacity 0.15s;
}
.btn:disabled { opacity: 0.5; cursor: not-allowed; }
.btn-primary { background: #2563eb; color: white; }
.btn-primary:hover:not(:disabled) { background: #1d4ed8; }
.btn-outline {
    background: white;
    border: 1.5px solid #ddd;
    color: #333;
}
.btn-outline:hover { border-color: #2563eb; color: #2563eb; }

/* Category Selection */
.cat-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 16px;
}
.categories h2 {
    font-size: 16px;
    color: #555;
}
.btn-sm {
    padding: 4px 14px;
    font-size: 13px;
}

.cat-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    gap: 12px;
    margin-bottom: 24px;
}

.cat-card {
    border: 1.5px solid #ddd;
    border-radius: 6px;
    padding: 14px 16px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    cursor: pointer;
    transition: border-color 0.15s, background 0.15s;
    background: white;
}
.cat-card:hover { border-color: #2563eb; }
.cat-card.selected { border-color: #2563eb; background: #eff6ff; }

.cat-card-left {
    display: flex;
    align-items: center;
    gap: 10px;
}

.cat-card .name { font-size: 14px; font-weight: 500; }
.cat-card .count {
    font-size: 12px;
    color: #888;
    background: #f0f0f0;
    padding: 2px 8px;
    border-radius: 10px;
    white-space: nowrap;
}

.cat-card .check {
    width: 18px;
    height: 18px;
    border: 1.5px solid #ccc;
    border-radius: 3px;
    display: inline-block;
    flex-shrink: 0;
    position: relative;
}
.cat-card.selected .check {
    background: #2563eb;
    border-color: #2563eb;
}
.cat-card.selected .check::after {
    content: "\2713";
    color: white;
    font-size: 12px;
    position: absolute;
    top: -1px;
    left: 3px;
}

.controls {
    padding: 16px 0;
    border-top: 1px solid #eee;
    display: flex;
    gap: 16px;
    align-items: center;
    flex-wrap: wrap;
}
.controls select {
    padding: 8px 12px;
    border: 1.5px solid #ddd;
    border-radius: 4px;
    font-size: 14px;
    background: white;
}
.controls .btn { margin-left: auto; }

/* Practice Mode */
.practice { padding: 8px 0; }

.progress-bar {
    height: 4px;
    background: #e9ecef;
    border-radius: 2px;
    margin-bottom: 12px;
}
.progress-bar .fill {
    height: 100%;
    background: #2563eb;
    border-radius: 2px;
    transition: width 0.3s ease;
    width: 0%;
}

.progress-info {
    display: flex;
    justify-content: space-between;
    font-size: 13px;
    color: #888;
    margin-bottom: 20px;
}

.question-card {
    background: white;
    border: 1.5px solid #ddd;
    border-radius: 8px;
    padding: 24px;
    margin-bottom: 20px;
}

.q-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 16px;
}
.q-number { font-size: 13px; color: #2563eb; font-weight: 600; }
.q-category {
    font-size: 12px;
    color: #888;
    background: #f0f0f0;
    padding: 2px 10px;
    border-radius: 10px;
}

.q-text {
    font-size: 15px;
    line-height: 1.7;
    margin-bottom: 20px;
}

.option {
    border: 1.5px solid #ddd;
    border-radius: 6px;
    padding: 12px 16px;
    margin-bottom: 8px;
    font-size: 14px;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 10px;
    background: white;
    transition: border-color 0.15s, background 0.15s;
}
.option:hover { border-color: #2563eb; background: #fafbff; }

.option .circle {
    width: 18px;
    height: 18px;
    border: 1.5px solid #ccc;
    border-radius: 50%;
    flex-shrink: 0;
}

.option.correct {
    border-color: #16a34a;
    background: #f0fdf4;
    cursor: default;
}
.option.correct .circle { background: #16a34a; border-color: #16a34a; }

.option.wrong {
    border-color: #dc2626;
    background: #fef2f2;
    cursor: default;
}
.option.wrong .circle { background: #dc2626; border-color: #dc2626; }

.answer-feedback {
    padding: 16px;
    border-radius: 6px;
    margin-top: 16px;
}
.answer-feedback.correct {
    background: #f0fdf4;
    border: 1px solid #bbf7d0;
}
.answer-feedback.incorrect {
    background: #fef2f2;
    border: 1px solid #fecaca;
}
.answer-feedback .label {
    font-size: 13px;
    font-weight: 600;
    margin-bottom: 6px;
}
.answer-feedback.correct .label { color: #16a34a; }
.answer-feedback.incorrect .label { color: #dc2626; }
.answer-feedback .regulation {
    font-size: 13px;
    color: #555;
    line-height: 1.5;
}

.nav-buttons {
    display: flex;
    justify-content: space-between;
    gap: 12px;
}

/* Results */
.results { padding: 8px 0; }

.score-card {
    text-align: center;
    padding: 32px;
    background: white;
    border: 1.5px solid #ddd;
    border-radius: 8px;
    margin-bottom: 24px;
}
.score-card .score { font-size: 48px; font-weight: 700; color: #2563eb; }
.score-card .label { font-size: 14px; color: #888; margin-top: 4px; }

.stats-row {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 12px;
    margin-bottom: 24px;
}
.stat-box {
    text-align: center;
    padding: 16px;
    background: white;
    border: 1px solid #eee;
    border-radius: 6px;
}
.stat-box .num { font-size: 24px; font-weight: 600; }
.stat-box .desc { font-size: 12px; color: #888; margin-top: 4px; }
.stat-box.green .num { color: #16a34a; }
.stat-box.red .num { color: #dc2626; }

.category-breakdown {
    background: white;
    border: 1px solid #eee;
    border-radius: 6px;
    overflow: hidden;
    margin-bottom: 24px;
}
.cb-header {
    padding: 12px 16px;
    background: #f8f9fa;
    font-size: 13px;
    font-weight: 600;
    color: #555;
    border-bottom: 1px solid #eee;
}
.cb-row {
    padding: 10px 16px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid #f0f0f0;
    font-size: 13px;
}
.cb-row:last-child { border-bottom: none; }

.cb-right {
    display: flex;
    align-items: center;
    gap: 8px;
}
.cb-bar {
    width: 120px;
    height: 6px;
    background: #e9ecef;
    border-radius: 3px;
}
.cb-bar .fill { height: 100%; border-radius: 3px; }
.cb-bar .fill.high { background: #16a34a; }
.cb-bar .fill.mid { background: #f59e0b; }
.cb-bar .fill.low { background: #dc2626; }
.cb-score { font-size: 12px; color: #888; min-width: 36px; text-align: right; }

.result-actions {
    display: flex;
    gap: 12px;
}

/* Section title */
.section-title {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 20px;
    color: #333;
}

/* Empty state */
.empty-state {
    text-align: center;
    padding: 60px 20px;
    color: #666;
    font-size: 15px;
}
.empty-state .btn { margin-top: 16px; }

/* AI Explanation */
.explain-btn { margin-top: 12px; }
.explanation-content {
    margin-top: 12px;
    padding: 16px;
    background: white;
    border-left: 3px solid #2563eb;
    border-radius: 0 6px 6px 0;
    font-size: 14px;
    line-height: 1.7;
    color: #333;
    white-space: pre-wrap;
}
.explanation-content.loading {
    color: #888;
    font-size: 13px;
    background: #f8f9fa;
    border-left-color: #ccc;
}

/* Utility */
.loading { color: #888; text-align: center; padding: 40px; }

/* Responsive */
@media (max-width: 600px) {
    .cat-grid { grid-template-columns: 1fr; }
    .stats-row { grid-template-columns: 1fr; }
    .controls { flex-direction: column; align-items: stretch; }
    .controls .btn { margin-left: 0; }
    .header { flex-direction: column; gap: 12px; align-items: flex-start; }
    .score-card .score { font-size: 36px; }
}