Wrong text color when hovering buttons on the 404 page

Moving the mouse over buttons on the 404 page makes the text the same color as their background:

The image shows a screen from a Discourse forum with error message "Oops! That page doesn't exist or is private" and a "Log In" button. (Captioned by AI)

The buttons’ focus state is ok and doesn’t display the issue.

The issue doesn’t occur with the search button at the very bottom of the page.