Consolidate buttons CSS into a single file
|Reported by:||koopersmith||Owned by:||koopersmith|
The button updates added in #21598 have made the code quite modular, but it is currently split between wp-admin.css and the two colors files (which have identical copies of the bulk of the buttons CSS). This is not particularly maintainable, and makes it impossible to use the buttons outside the context of the admin.
Given our plans for #21813, we'll need to reuse this CSS inside TinyMCE, and redeclaring the same code for the third time just seems silly.