This addon is a plugin. You need to extract it to your /plugins folder to install it.
I packaged up DraganBabic's great idea for Category Icons via stylesheet changes into an extension. This removes the need to change the vanilla.css file. I have included a set of images that I use for my categories. Replace them with your images. Then modify the included style.css file before uploading to your forum.
version 1.0.3 - added check of config version in order to add config setting and avoid unnecessary database access