You can also have a look at Atlas UI and the helper page.
All new Mendix projects are based on our Atlas UI frame work so you can use all the building blocks and widgets.
Mendix styling is based on Bootstrap, so any Bootstrap class should work.
There's also a nice list of all the possible classes you can set from bootstrap here:
https://www.w3schools.com/bootstrap/bootstrap_ref_all_classes.asp
https://ux.mendix.com is also a good source of what is possible.