TinyMCE has various different settings to really customize its features. One of these very useful settings is the ability to provide your own custom CSS classes for the editor itself. That way if you have, for example, modified the style of heading1, then you can provide that CSS to tinyMCE; that way, when you are editing, you truly get the full power of the "WYSIWYG" as the heading1 will look the same in the editor as it will when the HTML is generated.

There is a lack of architectural specifications when it comes to CSS. The biggest reason for this is probably because developpers see CSS more as a tool than a language. For example, we can all use a pen to write a word and get the job done. But none of us will ever write that word exactly the same. Everyone has a unique writing style. This is the same when it comes to CSS. We all write the same keywords, but developers always end up writing their CSS in a different way.