Add `class` alts for `aria-labels`

Fixes #91

In this PR:

Added styling class alternatives for title bar buttons' aria-label styling selectors.
Updated documentation to include example of styling class alternatives.

📈 Impact

Should this PR work as intended, users can now have title bar buttons' aria-labels be in languages other than English, such as the issue's example of using aria-label="Schließen" for a Close button, without causing rendering, accessibility, or localization issues.

📔 Dev Note

I believe that having an example of class and aria-label being used together to show that you can render buttons without completely relying on English text could be helpful. However, I did not know what would be the best way to do this in the documentation. I was thinking of using the issue's example with a window with only a close button, but I'm not certain. If this example seems good, I can add that to this PR.

jdan / 98.css