main>div {
    width: 640px;
    display: block;
    margin: 0 auto;
}

.section>div>div>input[type=text],
.section>div>div>input[type=email],
.section>div>div>input[type=password],
.section>div>div>textarea,
.section>div>div>select {
    width: 100%;
}

@media only screen and (max-width: 688px) {
    main>div {
        width: 100%;
    }
}