Instructions? Examples?

You’re probably going to laugh, but could you give some clue how to use this?
I have H%P installed and, for example, I want to change the font in the “Drag the Text” content type.

I know enough about css to have changed my theme by adding this in WordPress’s “Additional CSS”:

.site-title {
    font-family: comfortaa;
		font-weight: 700;
}

But how does one know what the classes/elements are in H5P?

Thank you!