html,
body {
    min-height: 100%;
}

body {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

body > .site-header,
body > .site-footer {
    flex: 0 0 auto;
}

body > main#main {
    flex: 1 0 auto;
    width: 100%;
}

@media (max-width: 700px) {
    body > main#main.page-main {
        width: calc(100% - 40px);
    }
}