:root {
    --primary: #2563eb;
    --primary-dark: #1d4ed8;
    --success: #16a34a;
    --warning: #d97706;
    --danger: #dc2626;
    --bg: #f8fafc;
    --card-bg: #ffffff;
    --text: #1e293b;
    --muted: #64748b;
    --border: #e2e8f0;
}

body {
    background: var(--bg);
    color: var(--text);
    font-family: 'Inter', system-ui, sans-serif;
}

.navbar-brand {
    font-weight: 800;
    font-size: 1.4rem;
    letter-spacing: -0.5px;
}

.card {
    border: 1px solid var(--border);
    border-radius: 12px;
    box-shadow: 0 1px 3px rgba(0,0,0,0.06);
}

.stat-card {
    text-align: center;
    padding: 1.5rem;
}

.stat-number {
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--primary);
}

.score-display {
    font-size: 5rem;
    font-weight: 900;
    line-height: 1;
}

.score-low { color: var(--danger); }
.score-mid { color: var(--warning); }
.score-high { color: var(--success); }

.difficulty-bar {
    height: 8px;
    border-radius: 4px;
    background: #e2e8f0;
}

.difficulty-fill {
    height: 100%;
    border-radius: 4px;
    background: linear-gradient(90deg, #16a34a, #d97706, #dc2626);
}

.table th {
    background: #f1f5f9;
    font-weight: 600;
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    color: var(--muted);
}

.btn-primary {
    background: var(--primary);
    border-color: var(--primary);
    font-weight: 600;
    padding: 0.6rem 1.5rem;
    border-radius: 8px;
}

.btn-primary:hover {
    background: var(--primary-dark);
    border-color: var(--primary-dark);
}

.tag {
    display: inline-block;
    padding: 0.2rem 0.6rem;
    background: #eff6ff;
    color: var(--primary);
    border-radius: 6px;
    font-size: 0.8rem;
    font-weight: 600;
    margin: 2px;
}

.spinner-overlay {
    display: none;
    position: fixed;
    top: 0; left: 0; right: 0; bottom: 0;
    background: rgba(255,255,255,0.8);
    z-index: 9999;
    justify-content: center;
    align-items: center;
}