In my Firefox 81.0.1 64-bit, on Windows 10 Pro 64-bit, the scroll buttons in the Similar Questions list on the Ask Question page (and also in code blocks everywhere else) are invisible:
That scrollbar wouldn't go up any further. I wondered about this, and @JohnDvorak explained that the buttons are invisible, and that it was by design, which is confirmed here. This also happens with the question body when there is enough content to merit a scrollbar.
With due respect, it is a terrible design choice to make a button that is functioning and clickable invisible. Can we please revert this?
@TylerH's Stylus solution works very well. Codeblock scrollbars:
And the scrollbar-buttons in the question body:
@Ygoe's solution (it too is Stylus) should also be noted. Both do the job, and are very simple fixes. Thanks Tyler, Ygoe!