buy button styling

This plugin was recommended to me and I am just setting everything up.
https://www.lassal.com/book-table/
Of all the different solutions I am testing on various sites, I am liking this one best so far.

Thanks to the universal buy button I can add some international sites, BUT it does not look too good with the disparate button styles. Also, I do not find any of the provided button-styles very appealing.

Is there a way for me to specify buy-buttons of my own, or at least make all of them look similar?
It does not look very elegant as it is right now.

(by the way, shadow-box does not seem to be working on Elegantthemes/Divi – it just does not show up at all.)

Thanks!

https://www.ads-software.com/plugins/mybooktable/