Gtk.StyleContext.prototype.get_section

function get_section(property:String):Gtk.CssSection {
    // Gjs wrapper for gtk_style_context_get_section()
}

Queries the location in the CSS where property was defined for the current context. Note that the state to be queried is taken from Gtk.get_state.

If the location is not available, null will be returned. The location might not be available for various reasons, such as the property being overridden, property not naming a supported CSS property or tracking of definitions being disabled for performance reasons.

Shorthand CSS properties cannot be queried for a location and will always return null.