It might be lack of sleep, but I can't figure this out.

I have a Label, and I want its text to be red when it represents an error, and I want it be green when it represent "good to go".

I found search result for C and maybe a solution for Python, but nothing for Rust.

I tried manually setting the css-classes property and running queue_draw(); it didn't work.

I can have a gtk::Box or a Frame that I place where the Label should go, then declare two Labels, and use set_child() to switch between them, but that seems like an ugly solution.

Do you have a solution?

SOLVED:

I have to add a "." before declaring a CSS "thing" for it to be considered a class.

Ex:

.overlay {
        background: rgba(60, 60, 60, 1);
        font-size: 25px;
}

instead of:

overlay {
        background: rgba(60, 60, 60, 1);
        font-size: 25px;)
}

Just use label.add_css_class(), label.remove_css_class() or label.set_css_classes() and make sure to properly load your CSS style sheets,

Source: the comment of d_k_bo@feddit.org