Hi! Thank you very much!
This was a good bit of work, because I was not familiar with the CSS syntax at all at the time, haha. I've made a gradient while experimenting with different shades of color combinations, then used a function to make it move, added some other small details to it.
If you like to get an exact button hassle free and some other details to make similar visuals, you can check out my resource package. A generalized version of my CSS styles is included into the custom CSS package and is available in this resource pack: https://pizzadoggy.itch.io/make-stuff-like-mine