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

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

.container {
    width: 100%;
    max-width: 500px;
}

.calculator-card {
    background: white;
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
    animation: slideIn 0.5s ease-out;
}

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

h1 {
    color: #333;
    margin-bottom: 30px;
    text-align: center;
    font-size: 2rem;
    font-weight: 600;
}

.form-group {
    margin-bottom: 25px;
}

label {
    display: block;
    margin-bottom: 8px;
    color: #555;
    font-weight: 500;
    font-size: 0.95rem;
}

input[type="number"],
input[type="text"] {
    width: 100%;
    padding: 12px 16px;
    border: 2px solid #e0e0e0;
    border-radius: 10px;
    font-size: 1rem;
    transition: all 0.3s ease;
    outline: none;
}

input[type="number"]:focus {
    border-color: #667eea;
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
}

input[type="text"][readonly] {
    background-color: #f5f5f5;
    cursor: not-allowed;
    color: #333;
    font-weight: 600;
}

.multiply-button {
    width: 100%;
    padding: 14px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    border: none;
    border-radius: 10px;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    margin-bottom: 25px;
    box-shadow: 0 4px 15px rgba(102, 126, 234, 0.4);
}

.multiply-button:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(102, 126, 234, 0.6);
}

.multiply-button:active {
    transform: translateY(0);
}

.multiply-button:disabled {
    background: #ccc;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

.error-message {
    color: #e74c3c;
    font-size: 0.9rem;
    margin-top: 10px;
    min-height: 20px;
    text-align: center;
}

@media (max-width: 600px) {
    .calculator-card {
        padding: 30px 20px;
    }
    
    h1 {
        font-size: 1.5rem;
    }
}