I know there have always been lingering issues with the HTML Composer, and that the one in version 8 is improved, but there's still a few things that I think could make it even better. Feel free to chime in with your own ideas!
I just recently uncovered a bug with Panels (possibly other controls) whereby App Studio crashes if I try to unset the inline styles (in the Properties pane) so that I can use a stylesheet. Example: If I put in a panel, and then a panel inside that to use as the panel heading, if I change Position to Relative (the default in HTML) and then either unset or set to Auto the height and width, then when I try to select that panel, App Studio crashes.
This brings up a more general thing about the Composer being fine if you're content to just do things WYSIWYG and modify inline CSS on every element, but for someone with an HTML background, it can get frustrating when trying to do things according to current web standards. For example, in my own coding I would never set inline styles on anything, I use stylesheets. So unsetting properties in the composer should pretty much do nothing, since it should be just going back to HTML defaults, and it probably is, it's just that the Composer (or App Studio itself, or both) can't select that element again.
A second idea: the HTML Composer should really have a tab back for view-only (at least) of the HTML code, which would help with debugging and in seeing what's going on (again, for people like myself who have some knowledge of HTML and CSS). I get that for version 8 you wanted to protect people from themselves as far as modifying the code, but it would still be good to be able to see what's being generated without having to go into the portal and editing from the Resource Tree.
All of this has stemmed from just wanted a nice, modern-looking HTML page (without those dark default gradients and inline styles) and using something like Bootstrap is a convenient way to do that. And I got it to work, but you have to do it right the first time, or else scrap it and start over, which seems to be something of a recurring theme I've noticed with the Composer in my past couple years of using it. Things go wrong for apparently no reason (especially when it comes to parameters), something gets set or unset, and there's no visibility into what's going on, which necessitates starting over and building it again from scratch, which is time-consuming, and should be unnecessary.
Well, that's long enough for here, looking for others to chime in with suggestions on what might make the HTML Composer in App Studio better (and please give a quick explanation of your HTML/CSS expertise when posting).
Prod: 8.2.0.4 OS:Windows 10 Output:AHTML, Excel 2007+
The life of a designer is a life of fight against the ugliness.