Wiki: Prevent button outline from being cut off in sidebar

What does this MR do and why?

This MR fixes an issue where the focus outlines on buttons would appear cut off in the wiki sidebar

References

fixes #584112

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open or create a wiki
2. Open the sidebar and navigate it with tabs
3. To view the chevrondown, create a custom sidebar

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.