I've been able to follow the instructions from the 2nd link pretty easily. I've been able to create tiddlers with single colors, change their opacity, and add background images from an external URL. One thing that is eluding me though, is how to add a background image from an an image that already exists in the wiki. For instance, I have a tiddler named image.png that is of type "image/png". When I use "background-image: url(./image.png);" in my stylesheet, it doesn't show up in the background of the test tiddler I want to apply it to. If I change the source to the URL of an image I see on the internet, it shows up just fine.