Dan,
Have you used Editor.EditorWysiwygModeCss Property specify the style sheet that will be used by the editable area?
If so, can you post the content of your style sheet?
Editor.EditorWysiwygModeCss Property
Specifies the location of the style sheet that will be used by the editable area. Multiple Style Sheets are supported. Example EditorWysiwygModeCss="example.css,~/portal.css,/default.css"
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