Working with roll20 Custom Sheets

I have been working on trying to convert Arcane Codex  to the Bethorm RPG. 

After spending some time translating and rewriting the HTML, I found that it just doesn’t run like the original although the Preview in the roll20 Custom Sheet area looks fine. 

I also found that if I copy and paste the the HTML, CSS and json into the Custom Sheet fields, it doesn’t display the way it should. 

Original:

Arcane Codex 2e

What I get when I copy and paste the same code into roll20: