Hi! You are trying to edit the exported CAS files of your game right? Also another question, you're using the latest versione if the engine?
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It's quite strange or meant I misunderstood your question. This is how you edit the style of your exported game: export your game, unzip it, open the style.css, and then modify it. You can use the CSS templates for reference. Or if you can, share some screenshots so I can better understand what is the issue :)