code: private void setItemOffsetsForHeader(Rect itemOffsets, View header, int orientation) {
          mDimensionCalculator.initMargins(mTempRect, header);
          if (orientation == LinearLayoutManager.VERTICAL) {
              itemOffsets.top = header.getHeight() + mTempRect.top + mTempRect.bottom;
          } else {
              itemOffsets.left = header.getWidth() + mTempRect.left + mTempRect.right;
          }
      }
docs: Sets the offsets for the first item in a section to make room for the header view
  
  @param itemOffsets rectangle to define offsets for the item
  @param header      view used to calculate offset for the item
  @param orientation used to calculate offset for the item