Fix editor.css to properly override all default TinyMCE styles from skin.min.css

[azaozz]

The editor.css stylesheet is meant to override some of the default TinyMCE UI styling. It is loaded last in Classic Editor (mid-page, after we know there is an editor there), but in the Block Editor it is loaded in the head. That exposes few selectors in editor.css that still depend on the loading order.

[azaozz]

There are few (mostly visual) bugs in the Classic Block because of that, see: ​https://github.com/WordPress/gutenberg/pull/10281.

Will try to patch it before 5.1-RC :)

[azaozz]

In 46164.diff: make the selectors in editor.css slightly more specific. Fixes styling problems in the Classic Block where editor.css is loaded early.

[azaozz]

Thinking more about this, currently for the Classic Block we do overrides of the overrides of the default TinyMCE styles. Best would be to fix/refactor editor.css to remove all these "second level" overrides. Opened https://core.trac.wordpress.org/ticket/46173 for that.

This ticket should focus only on fixing known bugs in the Classic Block styling for 5.1. Patch coming up.

[azaozz]

In 46164.1.diff: fix (visual) regressions in the Classic Block TinyMCE drop-down menu colors.

[azaozz]

In 44724:

TinyMCE: fix color of highlighted drop-down menu items in Classic Block.

Fixes #46164.