Fix dark mode for table

[koppor]

Follow-up to #11579

Dark mode was not working. I tried to use very dark colors now:

More changes:

• When hovering on a focused line, the text color changes (to indicate the hover activity - otherwise, there is no hovering feedback)
• Cleanup Base.css and MainTable.css
• introduce -jr-hover-text

Mandatory checks

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

Just for completeness, I played around to mark the search results using a darker color, but then without any search, the entry table colros changed. That looked not good

[github-actions]

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[Siedlerchr]

light theme was also modified?

[LoayGhreeb]

Just a minor issue I noticed, when no item is selected, hovering over the first item gives it a different style compared to hovering over other items.

[koppor]

light theme was also modified?

Yes. Cleanup after yesterday's quick fix #11579

[koppor]

Just a minor issue I noticed, when no item is selected, hovering over the first item gives it a different style compared to hovering over other items.

Hahaha. This is a brain teaser.

It seems this item is focused, but the JabRef focus CSS does not trigger.

#FutureWork