Decoration decoration

What decoration to paint.

Commonly a BoxDecoration.

Source 

Decoration get decoration => _decoration;
void decoration=(Decoration newDecoration)

Source 

set decoration (Decoration newDecoration) {
  assert(newDecoration != null);
  if (newDecoration == _decoration)
    return;
  _painter?.dispose();
  _painter = null;
  _decoration = newDecoration;
  markNeedsPaint();
}