Make overflowed content scrollable

[Leilei332]

This PR closes #8523.

Add overflow-x: auto to tc-tiddler-body and tc-tab-content to make overflowed content scrollable, so that overflowed content can be handled correctly.

[github-actions]

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[Jermolene]

Thanks @Leilei332 – I wonder if this solution might lead to scrollable areas nested within other scrollable areas? If so, I'd be concerned that it will be hard for us to assess usability across all the relevant browsers. For example, browsers configured to always show visible scrollbars might be confusing (which is already an issue with the sidebar implementation).

[Jermolene]

Hi @Leilei332 I think we should merge this. While I have reservations about the fix, it is a lot less broken than the current behaviour. I'd be grateful if you could resolve the merge conflict. Many thanks.

[Leilei332]

@Leilei332 -- It seems the latest changes have completely removed the tabs from all CSS rules. Is that intended?

I have fixed it. This is because I typed < in vim by mistake.

[Jermolene]

Thanks @Leilei332

[Leilei332]

Looks like tc-scary-warning is not compatible with this PR:

Before:

[Jermolene]

Ouch thanks @Leilei332 do you have time to work on a fix?

[Jermolene]

Looks like tc-scary-warning is not compatible with this PR:

On further investigation, I am inclined to think that we need to revert this PR. The ability to place content in the margins of tiddlers is important for some layouts, and so I think introducing a new scrolling context is too much of a break in backwards compatibility.

The revert is in 695e2ee

I'd welcome further exploration of a better fix.

[Leilei332]

Looks like overflow often occurs in elements like table and table of content macros. I think it may be better to only make them scrollable on overflow.