.calculator {
    background-color: #333;
    border-radius: 10px;
    padding: 20px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.2);
    text-align: center;
    color: #fff;
}

#display {
    width: 100%;
    padding: 10px;
    margin-bottom: 10px;
    font-size: 20px;
    background-color: #444;
    border: none;
    border-radius: 5px;
    color: #fff;
    text-align: right;
}

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

.btn {
    padding: 10px;
    font-size: 18px;
    border: none;
    border-radius: 5px;
    background-color: #555;
    color: #fff;
    cursor: pointer;
    transition: background-color 0.3s ease;
}

.btn:hover {
    background-color: #777;
}