I love UIAppearance. I am not too well versed in CSS but UIAppearance adds a lot of what I have seen done with CSS. You can change the default appearance of most default elements really easily, and declare containers inside of that with a whole different set of defaults. It makes styling your app a really painless process. All you have to do to make all the UIToolbars in your app red, for example, is use this one line at the start of your program.

  [[UIToolbar appearance] setTintColor:[UIColor redColor]];