You write that …
I created a category dynamic page using Wix data ,
… but on the pic 2-datasets are presented.
Sure that you have used Wix-Data? Or maybe it was a → DATASET?
Wix-Data and DATASET, are two different things, not recommended to mix them.
And if you really have used → Wix-Data, why you do not show us the related code, for debugging?
So, when reading this line…
How can I change the button color or button text color for a selected category as a dynamic page item?
I assume you are NOT working with → Wix-Data, instead you are working with → DATASETs (ordinary one and a dynamic one), right?
I think this is what you are searching for…
https://www.wix.com/velo/reference/$w/button/style