body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    font-family: sans-serif;
    background: #f2f2f2;
}

.calculator {
    border: 2px solid #444;
    padding: 1rem;
    border-radius: 8px;
    background: white;
    width: 250px;
}

#display {
    background: #eee;
    padding: 1rem;
    margin-bottom: 1rem;
    text-align: right;
    font-size: 2rem;
    border-radius: 4px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.5rem;
}

button {
    padding: 1rem;
    font-size: 1.2rem;
    border: none;
    border-radius: 4px;
    background: #ddd;
    cursor: pointer;
}

button.operator {
    background: #f7b731;
    color: white;
}

button.equal {
    grid-column: span 3;
    /* makes "=" button twice as wide */
}