Assistance with my new layout

If anyone who's better at understanding the interconnectedness of LJ and CSS than I am (which wouldn't take much; I'm far better at comprehension of CSS than I am with LJ, quite frankly) and would like to look at the code for my new layout and explain to me why half of my friends only see a fuscous page with a header and sidebar... that'd be fabulous. I got the layout from thefulcrum and didn't change a whit of the code, though I'd hoped to change the color scheme just a smidge. It's close enough to my former one, though, so I've really grown to like it, but it's giving people on my flist fits. Thanks!