Module collapsing_header 

CollapsingHeader — a clickable header that shows/hides child content.

Composition

CollapsingHeader
  ├── Label (header text, drawn manually)
  └── child widget (shown when expanded, hidden when collapsed)

The triangle indicator is drawn as a path. Clicking anywhere on the header row toggles the collapsed/expanded state.

Structs

CollapsingHeader

A collapsible section header. When expanded, the child widget is visible below the header row. When collapsed, only the header row is shown.