"And it's been right there, under my nose, the whole time!" This is you after I've revealed to you the solution to this "problem" (and this was my reaction, as well): how do you alter the out-of-the-box styling of your WYSIWYG editor in Drupal 8? How do you apply your own CSS styles without automatically modifying the CKEditor plugin settings (and without providing classes in the "Styles" menu)? It looks like the simplest solutions are both the most effective and the most difficult ones to notice. And where do you add that for this...