typo fixed: highligted source code of second radio button was missing

typo fixed: highligted source code of second radio button was missing in css.html -> checkboxes & radios -> default section

fix typo / doc components.html responsive menu dropdowns now have ref to...

fix typo / doc components.html responsive menu dropdowns now have ref to .dropdown-header instead of .nav-header

Restores `font-size` and more to the `<select>` element while also
changing from `min-height` to `height` for input sizing.

Fixes #8520 as opened by @ShaunR (would've merged that PR but I moved
everything around right before).

Documentation updates.

add comments to gloss Unicode codepoint hex

Conflicts:
	docs/assets/js/bootstrap.min.js

Remove unneeded prefixes from some mixins