How do I use the progress bar object?

I have tried in more instances than I am willing to admit to use the "Progress Bar" element without success. How do I change any of its styles? I can give it a class, but that appears to be referenced literally nowhere. The documentation is useless, and "set CSS style" and "set Attribute" don't work with any combination of "color", "background-color", "accent-color", and "red", "white", "#5050ff".

Can somebody explain this to me?

It's very easy to make your own progress bar using a sprite or tiled background. You literally only need a single action:

-> ProgressBar: Set width to Self.ImageWidth×progress

Where progress is a number from 0 to 1.

Here is a slightly more advanced example:

howtoconstructdemos.com/simple-healthbar