.em10 {
    background-color: #e4a;
    width: 10em;
    height: 2em;
}

.rem10 {
    background-color: black;
    width: 10rem;
    height: 2rem;
}

.bkpt1 {
    width: 300px;
    background-color: red;
}

.bkpt2 {
    width: 400px;
    background-color: green;
}

:root {
    color: aliceblue;
    font
}

@media (max-width: 500px) {
    .bkpt1 {
    width: 100vw;
     height: 100px;
     font-size:5rem;

    }
}