.calculator {
    max-width: 250px;
    margin: 0 auto;
    padding: 10px;
    border: 2px solid #ccc;
    border-radius: 5px;
    background-color: #f9f9f9;
}

.display {
    width: 100%;
    height: 40px;
    margin-bottom: 10px;
    text-align: right;
    font-size: 20px;
    padding: 10px;
    border: 1px solid #ccc;
    border-radius: 5px;
}

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

.btn {
    font-size: 18px;
    padding: 15px;
    background-color: #f0f0f0;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: background-color 0.3s;
}

.btn:hover {
    background-color: #e0e0e0;
}