Visual regression after gh-50 enabled permalinks for all headers

[erlend-aasland]

50 introduced a visual regression.

After #50:

Before #50:

See also:

• https://github.com/hpyproject/hpyproject.org/pull/50#discussion_r1534856787

[erlend-aasland]

@hodgestar https://github.com/hpyproject/hpyproject.org/pull/50#discussion_r1534939023:

Perhaps we can just style them better? Being able to link to subheadings on pages is nice.

[mattip]

Thanks for pointing it out. I only did half the sync with the pypy/pypy.org site styling, #52 should make it look better.