Function level_section 

pub fn level_section(
    area: Rect,
    label_count: usize,
    stepper_span: u16,
) -> Option<LevelSection>

Absolute geometry of the sidebar Level box, shared by the widget and the mouse hit-test so click targets cannot drift from what is drawn.

• area - the Level panel’s own bordered area, including its border.
• label_count - number of vertical levels; <= 1 hides the section.
• stepper_span - width of one stepper button (half the inner width).