Currently, if your institution has a theme style sheet, the styles are not viewable/applied in the Rich Content Editor while in Edit mode.  Only upon saving are you able to see styles applied from the theme style sheet.  I would like to propose that the RCE reflect the theme's style sheet while within the Rich Content Editor.  Here is the solution as provided by our IT personel:

"We believe the external CSS provided by the Customer via the Canvas Theme Editor within the context of a given Account/Sub-Account, as affecting the styles of a published Page, should also be included in the content_css array (https://www.tiny.cloud/docs/configure/content-appearance/#usingmultiplestylesheetsasarrayexample) of the TinyMCE editor upon initialization to accurately reflect within the Editor itself, the true styling of the resulting published Page."