I installed the update, but it didn't solve the problem.
The cause of the problem was the thread
W: Failed to fetch http://mirror.whonix.de/whonixdevelopermetafiles/internal/dists/jessie/main/binary-amd64/Packages HttpError404 which has such a long title that it messed up the CSS when it was in the "Latest" column. I manually edited the title (https://forums.whonix.org/t/w-failed-to-fetch-from-mirror-whonix-de/2022) and now the front page is back to normal. Probably worth filing a bug upstream.
Thanks for the initial report @HulaHoop!