#number-input {
    display: grid;
    grid-template-columns: repeat(3, 100px);
    grid-template-rows: repeat(4, 50px);
}

#number-input button {
    font-size: 1.25em;
}

div.input-group div.input {
    height: 21px;
}

div.input-group.selected {
    border: 1px red solid;
}