Hello. I hope that you are happy and well.
The nice Sitepoint book that started me on all this recommended that I have borders around all my divs while working, so I can see where things are. Which I think is a good idea and I like to do it. But some divs just refuse to display borders, and I can't find anywhere any kind of listings of what kinds of things would prevent a border from appearing. The css in the border-showing and non-border-showing categories looks the same.
What are the things that would make this happen?