body {
    font-family: Arial;
    text-align: center;
    transition: 0.3s;
}

body.dark {
    background-color: #121212;
    color: white;
}

body.light {
    background-color: #f4f4f4;
    color: black;
}

.calculator {
    width: 220px;
    margin: auto;
    padding: 15px;
    border-radius: 10px;
    background: #333;
}

body.light .calculator {
    background: white;
}

#display {
    width: 100%;
    height: 35px;
    font-size: 18px;
    text-align: right;
    margin-bottom: 10px;
}

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

.keys button {
    height: 50px;
    font-size: 18px;
    border-radius: 8px;
    border: none;
    cursor: pointer;
}

.clear {
    grid-column: span 4;
    background-color: #ff4d4d;
    color: white;
}