I had an app displaying all wrong in IE7.
Turns out it was a syntax error in the CSS, that other browsers (including IE8) were forgiving, but IE7 was not.
Yep, that’s an isolated single-quote on the end of the line, that shouldn’t be there. All the other browsers just ignored it, but I guess IE7 decided that it was a string open-quote, which wasn’t ever closed… and ignored all the CSS in the file after that point.
Removing that typo, and things display reasonably again, although there are still some annoying idiosyncracies displaying this page in IE7, the page isn’t a giant mess anymore.