body {
    background-color: bisque;
    display: flex;
    justify-content: center;
    font-family: Arial, Helvetica, sans-serif;
}

.calculator {
    overflow: hidden;
    width: 90%;
	height:100%;
    margin-top: 2rem;
}

.display {
    background-color: black;
    color: #fff;
    text-align: right;
    padding: 12px;
    font-size: 4em;
}

.payBtn{width: 20rem;padding: 30px; margin:30px 0px;}

.keys {
    display: grid;
    grid-template-columns: 1fr 1fr 1fr 1fr;
}

.btn-equal {
    background-color: chocolate;
    grid-column: 4;
    grid-row: 2 / span 4;
    color: #fff;
}

button {
    border: 0;
    outline: 0;
    padding: 10px;
    font-size: 2em;
}

.btn-operator {
    background-color: #ccc;
}