Import Local .css File

Hi, I wanted to use css locally in my folder, after visiting through example on github, for reference;
I didnt find any code to import css file locally. As it can see, the css file in folder of “assets” meanwhile file is the main code at the main folder. Thus, I need your help to clarify on this confused situation and where is the code to appoint css file locally?

María, see if this thread gives you the answer.

Okay, I will look into it. Thank you!