Add button, key styling like support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly

This allows for styling like in support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly

I noticed there is python code and tests which may be related.

Also I would like to field the idea to sort styles by name in ckeditor config (which I didn't do here).

It might go against muscle memory of frequent MDN editors, but would make the menu more explorable as it grows.

+  padding: 2px 8px