improve explore relevancy note

[crystalcommunication]

makes the explore relevancy note much prettier on most themes

[crystalcommunication]

The relevancy note box in the "Explore" section applies the "blue" class to the div element which seem to paint a blueish color to the background of the component, this may be undesirable depending on the user's theme.
The same box has inconsistency in the corners: rounded on top but sharp on bottom.
I'd also suggest detaching it from the search box, since the corners of the two boxes, being rounded, don't align correctly and don't look particularly good.

After and before in the screenshots, both with Forgejo dark theme.

Originally posted by @Gaarco in https://codeberg.org/Codeberg/Community/issues/885#issue-234675

before

after

requesting review from @Gusted

[wxiaoguang]

Why the class is not removed since the ui.explore-relevancy-note was deleted in _explore.less ?

[crystalcommunication]

I guess I thought it could be useful if a theme wanted to explicitly change the styling on it independently. I'm not particularly attached to it.

[delvh]

As you showed in
, is it really a good idea to remove the max-width restriction?
I think that style looked better than what you are proposing.

[delvh]

On the other hand, it is no longer attached so it does look fine.

[crystalcommunication]

I made the changes as proposed in the comment that I copied from Codeberg. I think it would look awkward being detached and also the same width as the search bar. When it was attached, @Gaarco made a great point about the borders being slightly misaligned and the rounded corners making it look weird if you pixel-peep. If you prefer it attached to the search box, perhaps we can adjust the styling to eliminate these issues instead.