Ok, since you did not reply, i did some investigations.
I now understand your suggestion → but this is still not what i was searching for and not a complete solution for a full dynamic resizing of en element on a wix-page.
1) Adding a → BOX → (checked).
2) Adding either a HTML-Comp. or Custom-Elem. into the BOX → (checked).
—> At this checkpoint → yes both of elements support the function.
3) Streching the inner-element to the BOX → (checked).
4) Adding generated CUSTOM-CSS to the → BOX → (checked)
But here we have again the STATIC (non-dynamic) problem.
You can set the CSS-Styles only → manually. You can’t define the CSS-Values dynamically by code. This is some-kind of a → SEMI-SOLUTION (partial solution).
You still have no real dynamic process-flow, because you can’t manipulate the CSS values dynamically by code. All you can do, is to add or replace → PREDEFINED <— CSS values.
Oh man! I hate this word —> PREDEFINED <— 
So you can provide maybe another solution → more dynamic?
Or do i have more options, regarding my issue?
I really do not want to recreate my already created and existing REPEATER-FUNCTION inside of my HTML-Comp. on a → Wix-Page ← to solve my problem.