[llvm] [Docs] Fix large vertical space at top of pages (PR #81599)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer commented:

I've not got a strong opinion on it either way, it's not my domain - but if nobody with more of investment in our css comes by to disagree, this LGTM (so safest to wait a bit for further comments).

https://github.com/llvm/llvm-project/pull/81599