The coding there actually allows everything to appear as your own…
Your own speech bubble (overlay) would appear instead of the Episode one because of the “0%” which renders the actual Episode bubble invisible. You could also choose to not insert a custom speech bubble overlay there if you don’t want any of your custom overlay narration/dialogue to come up) and the actual choice/option buttons are tappables which are also your own overlays (not the default episode ones).
Sorry if I sound confusing. I have my own custom overlays for example “Have you read this chapter?” in my own text (not a default bubble) and I also have the tappable options of “Yes.” and “No.” which are also custom overlays, I simply just added the gem part to it since that seems to be what you’re referring to? But that format allows just your overlays to appear instead of default bubbles/choice buttons.