I was looking into a fix for issues/10561 as a starter bug and a way to get more familiarity with the codebase. I was able to produce some style changes which addressed the issue, but I wanted to first verify that these were reasonable changes, and see if there was not other things that should be addressed for this issue.
And in light mode:
The text uses theme.color for the tab controls and an opacity of 0.8 for the inactive tab. This seems to follow in general the usage I saw for other areas, but for other cases where tabs / nav links are being used, there other background / highlight style changes that could be applied to make the dialog in general look more Joplin-themed, but this is a much bigger change than simply addressing text contrast. Secondarily, I didn't want to get into a lot of additional style and theme changes without first knowing if this might conflict with any other efforts, such as a TinyMCE version update. I didn't see any justification for the rollback to TinyMCE 5 in discussions elsewhere, but more style changes could compound any visual issues if that was the case.
This change is basically the bare minimum to address the bug. If you'd like to see any other changes in this PR let me know, otherwise I can send it for review as is.