Hola de nuevo @plusmartin , disculpa el retraso!
Here my answers:
where did you learn how to use CSS in glide?
Well, I started with basic functionality, I’m not a CSS master but I understood it better learning from some friends here.
You can read, learn and test using https://www.w3schools.com/cssref/default.asp as 1st option but pay attention: the use of CSS isn’t supported by Glide team, some code can be useful and make your APP looks very nice but if you abuse it, your APP can have some weird performance issues.
It’s like the sugar… enjoy it but don’t use it in every food 
do you have some examples of what is possible? you used it to move a button, some people use it to change background, etc
Well, this thread is our biggest toolbox to find and learn tricks or examples. Here you can see many options and solutions like you want to
Beautiful Design App.
Where can I see all the things that are possible and how to implement them?
This thread is a good place (I think) to begin and understand CSS world in Glide. It was very useful when floating button was not a native component yet but we started using it thanks @Jeff_Hager 's idea.
This is a wide and complex topic, start with what I have written you above if you want, later, go and test further features.
Un abrazo Martin!