I don't do it nowadays much, but I had to write some html and css.
I was just writing without checking anything. I only needed to do 5 pages. I wrote it, loaded, damn, not working. I went back, checked for all spelling, nothing wrong.
All right, let me try a different way for the css. Wrote the css pages again, no, no change at all. No spelling errors, no nothing. But there is something that it is not working. I went on line by line, no change. Removed most css, no change.
Hours later, I came back from outside, and opened the pages again, then I realized that I was using # and . in the wrong way.