You can embed images, using Markdown , same as here in Lemmy, also several themes. But yes, it isn't part of the fediverse.
Another possibility, if you have an own host, is using the Blue Velvet Editor, its a complete wordprozessor which works right in your browser (PC and Mobile), it saves the documents locally in Html format by default. So you can upload it as is to an host, as webpage. Free, private, no account and blazing fast.