I tried to analyze this once myself and quickly got lost in this maze of HTML and CSS. It's very inventive and hard to follow, so I guess it's hard to parse for a browser, too.

Just one example: On the main page, you see list items on a dark background with an orange triangle to the left. ("Active forums topics" is such a list.)
I got suspicous about this because usually I see this list with an orange background first, and it changes to black only when the page finished loading.

A look at the HTML+CSS makes me think (as I said, it's a maze, I'm not sure) that instead of simply setting the background to black, the code tells your browser to fetch this black image (2000x1000 pixels) and use it as background for each and every item in the list. The image is not completely black: If you look closely, you'll notice a tiny white spot in the upper right. That's the triangle, set to transparent, so the orange background I noticed will be visible here and create the illusion of a small orange triangle in front of each list item.

Also, there are shadow effects applied all over, so there's really a lot of nested DIV-containers and additional graphics to be loaded.