You shouldn't have to move the CSS file to get things working. Assume you have the following directory structure:
|
+--Css (folder)
| \--Stylesheet.css
|
+--Images (folder)
| \--image.jpg
|
\--Default.aspx
In your Default.aspx, you would do a link rel="stylesheet" referring to the css file with a
relative path of "Css/Stylesheet.css" just like you did.
Now, in your Stylesheet.css, in order to refer to an image, you need to go up one level (..) - since you're in Css folder, and then down in the Images folder. The path for this is "../Images/image.jpg".
If you have a directory structure similar to the one I've shown, things should work for you. Make sure you use forward slash (/) and not backslash (\) in paths.
If this post was useful to you, please mark it as answer. Thank you!