rpncalc/style.css

.rpncalc {
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
}

.item {
    width: 10vw;
    height: 10vw;
    border: 1px solid black;
    margin-bottom: -1px;
    display: flex;
    justify-content: center;
    align-items: center;
}

.exprinput {
    margin-bottom: 1vh;
}