Right now the buttons at the bottom of the form are wrapped in a <span class="mw-htmlform-submit-buttons"> tag. This span doesn't have any margins on it, and because the rest of the form fields have top margins, there's no spacing between the buttons and the form.
- Make this tag a div instead of a span (OOUIHTMLForm does this too)
- Style it to have a top margin of 16px (@spacing-100), but only in CodexHTMLForm