.main { margin-top: auto; margin-bottom: auto; margin-left: 0px; margin-right: 0px; position: relative; min-height: calc(100vh - var(--header-height) - var(--footer-height)); max-width: calc(var(--main-width) + var(--gap) * 2); padding: var(--gap); } *, ::after, ::before { box-sizing: content-box; } :root { --main-width: 100%; --main-height: 100%; } iframe { border: none; height: 100vh; /* 100% of view height */ width: 100%; }