tumblr css...

i swear i never had encountered this css before. I mean... I don't
know.... Never saw this before... I did looked into the tumblr css
customizing theme documentation and I couldn't find the anysimilar tag
declaration. Well, how i should describe the tag "background:
{color:Posts Wrapper Background Color};". Did it ever exist? Or I just
plain idiot that I haven't realize it exist. It's like the code is
trying to parse JSON to css. (well there was no quotation at the value
side) I looked on the internet and I don't found this similar css
declaration. Well, I don't know what happened here......