.calculator {
    background: purple;
    border: 1px solid #ccc;
    padding: 10px;
    width: 100%;
}

.display {
    background: #e8e8e8;
    border: 1px solid #bbb;
    padding: 10px;
    text-align: right;
    font-size: 20px;
    margin-bottom: 10px;
    min-height: 40px;
    overflow: hidden;
    word-break: break-all;
}

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

.key {
    font-family: Arial, sans-serif;
    font-size: 14px;
    padding: 4px;
    border: 1px solid #bbb;
    background: #fff;
    cursor: pointer;
}

    .key:hover {
        background: #e8e8e8;
    }

    .key:active {
        background: #d0d0d0;
    }

.key-eq {
    background: yellow;
    color: black;
    border-color: #b85a08;
}

    .key-eq:hover {
        background: #c86008;
    }

    .key-eq:active {
        background: #a85006;
    }

.display.error {
    color: red;
}