Dreamwidth style system discussion

I'm using 'Fluid Measure/Forest Green' as the theme. I changed the header by using the upload image under: Customize Your Theme: Style: Images: Header, but when I did the exact same thing to Page: Background, it stayed the default colors. I found a tutorial that said to go to the specific layer and theme, copy the raw source codes, and then change the background image to the URL of the image I want. I found both codes (Fluid Measure- http://www.dreamwidth.org/customize/advanced/layersource?id=80577) (Forest Green- http://www.dreamwidth.org/customize/advanced/layersource?id=174581), but have no idea what to change where. I read somewhere that you can change the background to transparent, but that I don't know how to do on DW.