I've just realized that it was impossible, or, anyway, it was beyond my capabilities.
There are too much different themes and different builders and different blocks in the WordPress ecosystem.
The goal of this plugin was to give the website creators a way to quickly and easily apply the same css
effect to ALL buttons of the project. But a button can be created with just a "span" element within a
"div" element, so detect all buttons becomes very hard (if not impossible).
In addition, it is very
difficult (if not impossible, once again) to create e css ruleset that can override any other rule
without breaking the integrity of the website layout and without run in compatiblity issues with other
css rulesets established by themes and/or plugins.
So, I decided to retire the plugin and to use it in my websites, where I can fine tune css rules depoending on the specific theme and plugins used in any specific website.
R.I.P.
If, for some reason, you want to contact me, you can do it using this contact form.