Examples: color mode enhancement

[louismaximepiton]

Description

Adding a theme toggle in each example.
Some small tweaks on some examples for the color mode.

Motivation & Context

Better change the color mode inside examples

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• (NA) I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-38144--twbs-bootstrap.netlify.app/docs/5.3/examples

Related issues

NA

Still todo

See if a fixed dropdown would be better.
Set a partial for this dropdown.
Need to be merged with #38058 ?

[julien-deramond]

I was thinking about it with the first version that uses the current color mode. Totally agree that this is way better to change it directly within the examples but I didn't know how.

Not a big fan of having an extra bar right now; especially in the navbars examples. But I can't find another way of doing it.

Another option could be to display the toggle in absolute position on a corner of the window; on top of everything in the same spirit as back-to-top buttons. But it might block the navigation in some use cases. And it should be accessible for keyboard users as well.

Or maybe something semi-hidden on the top right or left corner of the page like this skip links menu in Storybook (accessible and maybe with a bigger surface to see that there's actually something to click on):

[julien-deramond]

Thanks @mdo for 81f2f86. Sounds better, and less intrusive than a header.
@louismaximepiton I let you finalize the PR and I'll review it when it's ready but I like it already, very handful!

[mdo]

Thanks so much!