I have only used CSS to skin buttons for the most part, in your example I would add a State. You could then set the State programatically or on an event.
I added some stuff to the high contrast class ".headingText" and I don't see it ever being applied.
I should have pointed out that the Text fields I'm trying to work with are in a component. I don't know if that makes any difference and logic tells me it shouldn't, but just in case. I know the default style class works as I made that text green and it appears that way when run.
It would seem that if you reset css by selecting a different one that this different one doesn't propagate to the components of an application. To get around this problem, I added "setStyle"s to the function that adjusts the contrast. This also allowed me to remove the background color.
This was needed as the accessible part required high contrast. So I set the background to white for the black text. But when you go back to normal contrast, I had to remove the property completely so the underlying image would show again.