Great article. Love the interactivity. One thing that really helped me understand CSS positioning (and centering) years ago was reading about the box model. Understanding the box model helps you determine flow within the DOM. The `display` and `position` CSS properties are also fundamental to learning about positioning. MDN has great articles on these!
https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_...
https://developer.mozilla.org/en-US/docs/Learn/CSS/CSS_layou...