Up to 2020 the HTMLPreview action has only one text-edit that is a fixed height.
Given the basic structure of an HTML document a second text-edit could be useful to define the and the section in different fields.
This would add a layer of complexity to the action.
Maybe be there could be a list/stack of text-edits that the user can add. If the GUI would be similar to the action steps UI this would increase the usability of the HTML preview action by hiding long blocks of CSS or script code.
If something is to compact in the request please feel free to ask…