This is not the help desk for Stylus. The FCC forum is for people that are learning web development.
The Stylus documentation states
If you know CSS , you can write your own styles.
You do not know CSS so you will not be able to write your own styles.
The link to FreeCodeCamp in that statement was for people that might want to learn CSS. Since you don’t seem interested in learning CSS then there is really not much for you here.
That still leaves you with some choices though. You can find and use a style written by someone that does know CSS (and possibly alter it to your liking), you can Google “centering with CSS” and probably come up with an adequate solution, or you can reconsider you goals and dedicate some time to learning a minimum of CSS that will allow you create a Stylus stylesheet at some time in the near future.
A good first shallow pass would be to kill an afternoon going through this tutorial
Afterwards, if you’re still interested in learning web development consider FreeCodeCamp or a good book to further you CSS knowledge.