message: Scale scrollbar movement by content ratio
diff: @@ -102,8 +102,11 @@ where
  if let Some(scrollbar_grabbed_at) =
  self.state.scrollbar_grabbed_at
  {
  + let ratio = content_bounds.height / bounds.height;
  + let delta = scrollbar_grabbed_at.y - cursor_position.y;
  +
  self.state.scroll(
  - scrollbar_grabbed_at.y - cursor_position.y,
  + delta * ratio,
  bounds,
  content_bounds,
  );
  