Follow-up from "Restyle changes header & file tree"
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The following discussion from !23665 should be addressed:
- [ ] @pslaughter started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/23665#note_282444584): (+1 comment)
> **suggestion (non-blocking):** Could we consider making this `auto`... It currently looks like this for me:
>
> | Before (currently) | After (with `overflow-y: auto`) |
> |--------|-------|
> |  |  |
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