Example of STYLE_CLASS_* constants

[kornelski]

gtk has constants for STYLE_CLASS_*, e.g.

https://gtk-rs.org/docs/gtk/struct.STYLE_CLASS_TITLE.html

but:

• There's no documentation for them at all in rustdoc docs
• I don't see a way to see how they look
• There's no example code for them

For example, I need to different styles of labels for keys and values in my UI, but I don't know how to achieve that.

GTK says:

https://developer.gnome.org/gtk3/stable/GtkLabel.html

A wide variety of style classes may be applied to labels, such as .title, .subtitle, .dim-label, etc.

but that doesn't mean anything to me, because I don't know where I'm supposed to put .dim-label from Rust.