body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f0f0f0;
    margin: 0;
    font-family: Arial, sans-serif;
}

.calculator {
    background-color: #fff;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
    max-width: 400px;
    width: 100%;
}

.display {
    background-color: #333;
    color: #fff;
    font-size: 2em;
    text-align: right;
    padding: 10px;
    border-radius: 5px;
    margin-bottom: 10px;
    word-wrap: break-word;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

.btn {
    background-color: #f0f0f0;
    border: none;
    padding: 20px;
    font-size: 1.5em;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.3s ease;
}

.btn:active {
    background-color: #ddd;
}

.operator {
    background-color: #ff9500;
    color: #fff;
}

.operator:active {
    background-color: #cc7a00;
}

.equals {
    grid-column: span 2;
    background-color: #007aff;
    color: #fff;
}

.equals:active {
    background-color: #005bb5;
}

.zero {
    grid-column: span 2;
}

@media (max-width: 400px) {
    .btn {
        padding: 15px;
        font-size: 1.2em;
    }

    .display {
        font-size: 1.5em;
    }
}