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

body {
    font-family: Arial, sans-serif;
    background: #f2f2f2;

    display: flex;
    justify-content: center;
    align-items: center;

    height: 100vh;
}

.calculator {
    width: 320px;
    background: #222;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.3);
}

#display {
    width: 100%;
    height: 70px;

    margin-bottom: 15px;

    font-size: 30px;
    text-align: right;

    padding: 10px;

    border: none;
    border-radius: 8px;

    background: white;
}

.buttons {
    display: grid;

    grid-template-columns: repeat(4, 1fr);

    gap: 10px;
}

button {
    height: 60px;

    border: none;
    border-radius: 8px;

    font-size: 20px;

    cursor: pointer;

    background: #444;
    color: white;
}

button:hover {
    background: #666;
}

.clear {
    background: #d9534f;
}

.clear:hover {
    background: #c9302c;
}

.equal {
    background: #28a745;
}

.equal:hover {
    background: #218838;
}

.zero {
    grid-column: span 2;
}