Welcome, there.
I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.
You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.
See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).
Something that comes to mind is: Are you sure the path to the .jpg is correct? That is, if your CSS is in a different location to your HTML, then the relative path will need to be different.
The quickest way to tell would be to open the browser devtools, and look in the console for errors related to the image not being downloaded/found.
Hope this helps