A disappearing CKEditor box when you try to activate the buttons for Font selection, Font Size, Font Color, and Font Highlight is a continuing problem in Drupal 8. The solution was simple after I found an explanation by Wim Leers.
The video course that I took to get started in Drupal did a wonderful job of showing me how to create a custom block and put it in an area on my webpage. Unfortunately, I have since found that except in rare instances it's the wrong thing to do.