* {
    box-sizing: border-box;
}

body>* {
    border: 1px dashed black;
    padding: 0;
}

body {
    min-height: 98vh;
    display: flex;
    flex-direction: column;
}

main {
    flex-grow: 1;
}

@media (min-width: 768px) {
    main {
        width: 768px;
        margin: auto;
    }
}