Instead of this maybe we should just go ahead and support Qt property selectors for CSS.
```
WPushButton[displayValue="1"] {
  background-color: red;
}
```

The crappy thing is that you have to re-set the stylesheet every time since Qt CSS doesn't support dynamic update based on Qt properties. But if you are already re-setting the stylesheet on every value change then this is just as much of a performance hit as doing the general thing.