I know how to use css to use a custom image for the background of a website if i were making it myself from ground up, but wordpress only gives you one css page, and can't tell that you want to fetch an image from your computer.
Usually you would use:
but how does wordpress.com know where the image comes from? and how do you make it work? because when I typed:
and saved my custom css, it did nothing.
I use a pc and it would be great if anyone could help out a bit.