Each time you hit Redraw this will create 1000 divs each with a freshly calculated random style. These styles then get added to the style sheet. Obviously this is very workload heavy, typically seed style caches repeated styles therefore the stylesheet is only being hit on new styles. On a 2011 laptop in release mode this renders in 84ms for a fresh style-uncached render. If styles are cached, which is usually the case, this renders in 16ms.
Note #1: Not much work has yet gone into improving styling performance yet.
Note #2: Every time you hit redraw it adds 1000 styles to the app's stylesheet so you probably want to refresh after testing this!
Note #3: If this appears a little laggy you probably have built in debug mode the timing here is approx 450ms!.