Haxeui API

One thing I am not getting right.
So far, I know how to change the menubar’s backgroundColor, but how do I change the menu button’s color?

I thought this would do it.

		<style>
			.menu {
				width: 128px;
			}
			.button {
				font-size: 16px;
				backgroundColor: #3f3f3f
			}
		</style>

However, the color remains white.
The api reference indicates backgroundColor as one of its properties.

backgroundColor:Null

Or maybe I coded it incorrectly?