/* === RESET & BASE === */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
}

.container {
    width: 100%;
    max-width: 900px;
    background: white;
    border-radius: 20px;
    box-shadow: 0 20px 60px rgba(0,0,0,0.3);
    overflow: hidden;
}

/* === HEADER === */
header {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 30px;
    text-align: center;
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 10px;
}

.subtitle {
    font-size: 1.1rem;
    opacity: 0.9;
    margin-bottom: 15px;
}

.pool-badge {
    display: inline-block;
    background: rgba(255,255,255,0.2);
    padding: 8px 20px;
    border-radius: 20px;
    font-size: 0.9rem;
    font-weight: 600;
}

/* === STATISTICS === */
.stats {
    display: flex;
    justify-content: space-around;
    padding: 20px;
    background: #f8fafc;
    border-bottom: 2px solid #e2e8f0;
}

.stat-item {
    text-align: center;
}

.stat-label {
    display: block;
    font-size: 0.9rem;
    color: #64748b;
    margin-bottom: 5px;
}

.stat-value {
    display: block;
    font-size: 1.8rem;
    font-weight: 700;
    color: #1e293b;
}

.stat-value.success {
    color: #10b981;
}

.stat-value.error {
    color: #ef4444;
}

/* === PROBLEM BOX === */
.problem-box {
    padding: 30px;
    border-bottom: 2px solid #e2e8f0;
}

.math-display {
    font-size: 1.3rem;
    padding: 15px;
}

/* === CHOICES === */
.choices {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
    padding: 30px;
}

.choice-btn {
    padding: 20px;
    font-size: 1.1rem;
    background: white;
    border: 3px solid #e2e8f0;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.2s;
    min-height: 80px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.choice-btn:hover:not(:disabled) {
    border-color: #3b82f6;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(59, 130, 246, 0.3);
}

.choice-btn:disabled {
    cursor: not-allowed;
}

/* === BUTTONS === */
.start-btn {
    padding: 15px 40px;
    font-size: 1.3rem;
    font-weight: 600;
    background: #3b82f6;
    color: white;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.3s;
}

.start-btn:hover {
    background: #2563eb;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(59, 130, 246, 0.4);
}

/* === ANIMATIONS === */
@keyframes fadeInOut {
    0% { opacity: 0; transform: translate(-50%, -50%) scale(0.8); }
    50% { opacity: 1; transform: translate(-50%, -50%) scale(1.2); }
    100% { opacity: 0; transform: translate(-50%, -50%) scale(0.8); }
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

@keyframes scaleIn {
    from { 
        opacity: 0; 
        transform: scale(0.7);
    }
    to { 
        opacity: 1; 
        transform: scale(1);
    }
}

/* === RESPONSIVE === */
@media (max-width: 768px) {
    header h1 {
        font-size: 2rem;
    }
    
    .choices {
        grid-template-columns: 1fr;
    }
    
    .stat-value {
        font-size: 1.5rem;
    }
}