
Currently, PowerApps doesn't support CSS. So it's not possible apply Bootstrap/PrimeNG or SPFx Extension/Webparts in PowerApps.
Here is a similar question for your reference:
https://powerusers.microsoft.com/t5/Building-Power-Apps/Bootstrap-3-3-7-use-in-powerapps/td-p/411710
Besides, if you have more questions about powerApps, I would suggest you' better ask in the powerapps forums.
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