Function nav_group_button 

pub fn nav_group_button(
    ui: &mut Ui,
    group_icon: &'static str,
    group_label: &'static str,
    items: &[NavGroupItem],
    current_page: &mut Page,
) -> Response

Creates a navigation button that represents a group of pages.

On hover, it expands horizontally to show sub-options. On click, or Enter/Space when focused, it cycles through the pages. The popup itself never takes keyboard focus.