div[id="op1"] {
    background-color: lightskyblue;
    margin: 5px;
    padding: 10px;
}

div[id="op2"] {
    background-color: lightgreen;
    margin: 5px;
    padding: 10px;
}

div[id="but"] {
    background-color: palevioletred;
    margin: 5px;
    padding: 10px;
    display: flex;
    flex-direction: column;
    justify-content: center;
}

div[id="res"] {
    background-color: yellow;
    margin: 5px;
    padding: 10px;
}

input[type="number"] {
    background-color: yellow;
}

input[type="submit"] {
    background-color: deepskyblue;
}

input[type="reset"] {
    background-color: palevioletred;
}

.inline-divs {
    display: flex;
    flex-direction: row;
    align-items: stretch;
}