We were using an <a> tag wrapping the whole content of the banner in
order to make the whole banner clickable. However, that made the text of
the link less concise, affecting people using screen readers. So,
instead, we're using the `card` mixin, which we introduced in commit
f285dfcba.
We're making this change now because the HTML5 Sanitizer that we're
about to enable in the next commit was handling the whitespace inside
the banner differently, causing one test to fail, and we didn't find a
different way to fix it.
0dec47c055