Here it is.

Heavy css use implies the use of a lot of images. These are called through css. Create a directory structure within a styles directory. Doing so will allow the css system to be more self-contained for the webmaster. This might help increase portability. It might speed execution (my conjecture).

Any way, I did it such as:

.categoryMain {
background: #fff url(i/c.jpg) 0px 0px no-repeat;
padding: 15px;
}

But why even use subdirectories?
Continuing on this thought, why even use a subdirectory. Just place the images in same directory as the css file. Now you have a cleaner path for subsequent DOM moves. So now its:

.categoryMain {
background: #fff url(c.jpg) 0px 0px no-repeat;
padding: 15px;
}

Its still portable. You case rename the root directory to whatever later. I've always seemed to bumble my way around, especially calling images with css. This makes it simpler.