For example, if you copy and paste this code below into a "raw" block, a simple html webpage will show up. I want my users to be able to use this to create simple webpages. It just needs CSS and HTML. This is a great idea to allow people to create their own websites within a UNA site.
We certainly don't recommend giving users access to UNA Studio... :)
The Froala editor can probably be edited to do what you are looking for. You can edit the buttons available in Studio>Settings>Froala. Go to https://www.froala.com/wysiwyg-editor/examples/toolbar-buttons as take a look at what is possible there, you can add a button for CodeView, perhaps if that is all you want, you could remove all the WYSYWIG functions?