Following illustrates in an atomic fashion the use of margin:auto:
Again the description in the curriculum of the z-index property was perplexing & I did not grasp it entirely.
I had to actually see a demonstration to believe what position:fixed as an attribute and value for an html element in a style sheet can do:
In matters related to front end and CSS in particular illustrations are worth 10,000 words & clear up any confusion or claims in text.
So when I was just trying to shore up my understanding of CSS I was frustrated by the offering of the curriculum because it would touch on topics without illustrations or examples & I was not understanding what was going on but then it would quiz people or present labs on basic concepts that became difficult to solve because the background information was not provided.