body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    font-family: Arial, sans-serif;
    background-color: #f5f5f5;
}

.calculator {
    width: 300px;
    background-color: #333;
    border-radius: 10px;
    box-shadow: 0 0 20px rgba(0, 0, 0, 0.2);
}

.display {
    background-color: #444;
    color: #fff;
    font-size: 2em;
    text-align: right;
    padding: 10px;
    border-top-left-radius: 10px;
    border-top-right-radius: 10px;
}

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

button {
    background-color: #555;
    color: #fff;
    font-size: 1.5em;
    border: none;
    outline: none;
    cursor: pointer;
    padding: 20px;
}

button:active {
    background-color: #777;
}

button.double {
    grid-column: span 2;
}