basic CSS: allow more "floating"

[mgeier]

I wasn't aware of an IMHO very un-intuitive interaction between overflow and float: If an element has an overflow setting, preceding elements cannot "float" into it.

That's why I'm suggesting to remove the overflow setting from admonition and topic.

This partially reverts my previous PR #7542. I'm only keeping the overflow setting on sidebar, where "floating into it" is not desired anyway.

For the other elements, it looks like we cannot have perfect "overflow" and perfect "float" behavior at the same time.
Derived themes can still add their overflow settings if they want.

This also partially reverts my previous PR #7484. It allows "right floats" to float into admonition and topic elements (as was possible before #7484). It still doesn't allow floating into code blocks, because this would interact badly with their overflow behavior (which is more important).

Feature or Bugfix

• Bugfix

[tk0miya]

@mgeier Could you add a CHANGES entry please? I can't describe what is changed by this.

Note: I still don't understand what is happened now. So I'm just merging this...

[mgeier]

I've re-based this PR and added CHANGES in c40cb79.

There is no separate issue for this, one example for the problem has been reported in #7484 (comment)

The problem is that it's not possible to have overflow (i.e. scrollbars) on admonitions etc. (as I suggested in #7542) and at the same time allowing preceding elements (like sidebar) to "flow" into the admonition.

This PR partially reverts #7542 and #7484 to allow sidebar to "flow" into admonitions etc.

This is more in line with previous behavior (before #7542 and #7484). If a derived theme wants to enable overflow behavior (and thereby disable "float" behavior), it can still do that, but I think for the basic theme we shouldn't do that.

This PR also adds a so-called "clearfix" (in 3098aba) to avoid elements (like images) to "flow" out of the bottom of admonitions etc.

[tk0miya]

Thank you for the detailed explanation! Merged.