body {
    background-color: #f3f4f6;
    font-family: 'Inter', sans-serif;
}

input[type="number"] {
    transition: all 0.3s ease;
}

input[type="number"]:focus {
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.3);
}

button {
    transition: all 0.3s ease;
}

#result {
    transition: opacity 0.3s ease;
}

@media (max-width: 640px) {
    .container {
        padding: 1rem;
    }

    h1 {
        font-size: 1.5rem;
    }

    button {
        padding: 0.5rem 1rem;
        font-size: 0.875rem;
    }
}

.hidden {
    display: none;
}

.error {
    border-color: red;
}

.error-message {
    color: red;
    font-size: 0.875rem;
    margin-top: 0.25rem;
}