[clang-tools-extra] [clang-doc] fix overlapping navbar (PR #164314)

[Erick Velez via cfe-commits]

evelez7 wrote:

You can see the changes reflected here: https://erickvelez.com/clang-doc-mustache-output/pr164314/

The "Inner Classes" heading isn't covered by the navbar anymore. Also never noticed that on class pages, the class' name is actually displayed on top of the sidebar.

https://github.com/llvm/llvm-project/pull/164314