So, if I got this right, this doesn't show when both files (html and CSS) are on your computer, not on Codecademy?
I just tried setting this up on my desktop and everything works.
You'll have to make sure that both files are in the same folder, and that the link to the CSS sheet is correct. They don't necessarily have to be in the same folder, but for the sake of this exercise, let's do that.
Put index.html and style.css in the same folder.
Then, in your HTML document, make sure to modify the link to the CSS, like this:
<link href="style.css" type="text/css" rel="stylesheet" />
I just changed /style.css to style.css
That's basically what I did, and everything worked nicely. What puzzles me is that you said "the first background doesn't display". Does that mean the other two do show?