body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f4f4f4;
    font-family: Arial, Helvetica, sans-serif;
}

.calculator {
    width: 250px;
    border-radius: 8px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    padding: 20px;
    background: white;
}

#display {
    width: 100%;
    height: 50px;
    margin-bottom: 20px;
    font-size: 24px;
    text-align: right;
    border: 1px solid #ddd;
    border-radius: 5px;
}

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

.btn {
    padding: 15px;
    border: none;
    border-radius: 5px;
    background-color: #f0f0f0;
    cursor: pointer;
    font-size: 18px;
    transition: background-color 0.2s;
}

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

.clear {
    grid-column: span 4;
    background-color: #f8d7da;
}

.clear:hover {
    background-color: #f5b7b1;
}