message: Fix incorrect index when accessing Background Attribute (mac)
diff: @@ -141,8 +141,7 @@ final class TimelineFlowLayout: NSCollectionViewFlowLayout {
  return dividerAttributes[safe: indexPath.section]
  }
  if elementKind == NSCollectionView.elementKindSectionHeader {
  - let index = (indexPath.item / 2) + 1
  - return backgroundAttributes[safe: index]
  + return backgroundAttributes[safe: indexPath.item]
  }
  return nil
  }
  