Just for fun, here's a quick comparison of how the style sheet fares on the various Maemo browsers I have easy access to, ie :

Under Maemo4 (Diablo, N810) :
Micro-B (native, gecko-based)
Tear (third-party, Webkit-based)

Under Maemo4 (Fremantle, N900) :
Micro-B (native, gecko-based)
Firefox (third-party, gecko-based)
Macuco (third-party, Webkit-based)

Simply put, the N900 native browser is the worst of all, visually speaking, as far as reproducing the Fremantle UI is concerned. The blue background never appears while finger-scrolling a list around, only when actually selecting an item (ie just before changing pages...). If you look really close there is a dark grey background sometimes.

All others show the correct bg color while scrollling, even good old Diablo MicroB. Firefox on N900 is very choppy and leaves blue trails. Webkit-based browsers seem better at it : Tear is passable under Diablo, and Macuco is the overall winner on N900 : very fluid, and visually closest to the native UI.

So you thought the days of CSS-hell were behind us ? Think again :-)