body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    margin: 0;
    padding: 20px;
}

.container {
    background: white;
    border-radius: 20px;
    padding: 30px;
    box-shadow: 0 20px 60px rgba(0,0,0,0.3);
    text-align: center;
    max-width: 600px;
    width: 100%;
}

h1 {
    color: #667eea;
    margin-bottom: 5px;
}

.fecha {
    color: #999;
    font-size: 14px;
    margin-bottom: 30px;
}

.serie {
    font-size: 28px;
    font-weight: bold;
    background: #f0f0f0;
    padding: 20px;
    border-radius: 15px;
    margin: 20px 0;
    font-family: 'Courier New', monospace;
}

.interrogante {
    color: #764ba2;
    font-size: 32px;
}

.instruccion {
    font-size: 18px;
    margin: 20px 0;
}

.opciones {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(100px, 1fr));
    gap: 15px;
    margin: 30px 0;
}

.opcion {
    background: #667eea;
    color: white;
    border: none;
    padding: 15px 20px;
    font-size: 20px;
    font-weight: bold;
    border-radius: 10px;
    cursor: pointer;
    transition: transform 0.2s, background 0.2s;
}

.opcion:hover:not(:disabled) {
    background: #764ba2;
    transform: scale(1.05);
}

.opcion:disabled {
    cursor: not-allowed;
}

.mensaje {
    font-size: 18px;
    padding: 15px;
    border-radius: 10px;
    margin-top: 20px;
    min-height: 80px;
}

.debug {
    margin-top: 30px;
    padding: 10px;
    background: #f8f9fa;
    border-radius: 8px;
    font-size: 12px;
    color: #666;
}

@media (max-width: 500px) {
    .opciones {
        grid-template-columns: 1fr 1fr;
    }
    
    .serie {
        font-size: 20px;
    }
}