You can relate stylesheets to the richttext editor datatype in umbraco, sometimes this will cause an unwanted effect. Like a background color that you don’t want, …
But this can easily be changed.
You can target the richttext editor with the class
So by appending this to the related stylesheet, you have more control over the styling in the richttext editor datatype.
(make sure to clear your browser cache, to view the result)