Function ui_button_variant 

pub fn ui_button_variant(
    id: u32,
    x: f32,
    y: f32,
    w: f32,
    h: f32,
    label: &str,
    variant: UiVariant,
    on_click: impl FnOnce(),
)

Render a button with a specific UiVariant and run on_click when it is clicked.