[c-smile]

browsers do the following:

By given set of HTML and CSS produce bitmap on screen. That's perfectly determined task (modulo browser differences).

WYSIWYG editor does the opposite task:

With the given bitmap on screen produce set of valid HTML and CSS declarations.

The last task is undetermined mathematically speaking - with modern HTML and especially CSS there are too many ways of get the same rendering using completely different CSS tricks - absolute positioning, floats, display:grid and flexbox etc. etc.