body {
    font-family: Arial, sans-serif;
    background: #2c3e50;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.calculator {
    background: #ecf0f1;
    padding: 20px;
    border-radius: 10px;
    width: 250px;
}

.calculator h2 {
    text-align: center;
}

#display {
    width: 100%;
    height: 40px;
    font-size: 18px;
    margin-bottom: 10px;
    text-align: right;
    padding-right: 10px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 5px;
}

button {
    height: 40px;
    font-size: 16px;
    cursor: pointer;
}

.zero {
    grid-column: span 2;
}