[page descirption tag] need to fix a small spacing issue

[laurenmrice]

After approving this recent related Gatbsy PR (#1513), I realized that the spacing for this is not entirely correct yet once I saw it actually live in my own PR.

I noticed this because when switching between the Usage/Style/Code/A11y tabs, the height of the description jumps down the page because of the addition of the tag. The page description needs to stay in the same place across tabs even when the tag is present and its not accounting for the space below the tag as part of the full 80px.

Example gif of whats happening in my PR

Spec

What I believe it is not accounting for is including the extra 16px padding below the tag as part of the full 80px.