Hubitat has a document and video tutorial for all the basics.
HE Documentation
List of Compatible Devices (a great list of plug and play devices. This list is not definitive! There are also a lot of user made drivers to make it work.)
For some more difficult question/problems just type in google: "Hubitat topic/problem/device". Most of it is already documented 
For the CSS part:
The noobs in complete guide to css for hubitat
And anything you can find on: w3schools.com
A lot of text, but then again a lot of possibilities. Have a look at: "Show Off Your Dashboards!" in my first post.
