copy and paste the HTML, CSS and json into Custom Sheet fields doesn't display correctly

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 (when selected from the drop down list) although the Preview in the roll20 Custom Sheet area looks fine.  I also found that if I copy and paste the HTML, CSS and json into the Custom Sheet fields, it doesn't display the way it should (compare to original at link above).  Not well versed in HTML or CSS to make my own from scratch, but just dangerous enough to make small changes. But this doesn't make sense that the same code does work when it is copied and pasted. Any ideas that might help me along?

Have you tried switching between legacy and non-legacy (or vice-versa)? If you're running using the custom sheet, there's a checkbox. (Though there's nowhere to enter JSON there.)

Thank you, GiGs . That totally worked!!!    I was thinking that I wasted a few hours of work.   Legacy Sanitization Forces sheet to use the more limited legacy version of CSS and HTML sanitization. I guess the Arcane Codex sheet codes are really old versions. I learned something today.

There's a lot of sheets that use legacy sanitisation. While CSE was introduced a fairly long time ago now, actually updating an already-existing sheet to use it takes a lot of work, and many sheets are not actively maintained, and even for those that are, the developers often don't have the time or need to do this work. I always advise people creating a new sheet to use CSE, because the code is just better and takes (very marginally) less work, but for sheets that have been around a while, it's understandable why they still use Legacy code.