Follow up to #1890502: WYSIWYG: Add CKEditor module to core. That issue introduced a ckeditor.css file containing CSS such as:
When a content editor edits text via CKEditor and clicks the "align center" button to center align some text, this class gets added to the corresponding HTML.
Currently, because this CSS file resides in the CKEditor module, if you then disable that module, that CSS file is no longer output to the page. That's not desired: when a site builder disables the CKEditor module, they expect it to just mean that content can't be edited with CKEditor any more, not that content that had previously been edited with it will no longer retain any of its styling.
So, where should this CSS live? system.base.css?