Do you mean expander on the right and bold text by the "same style as we see in Files, Music, or Geary". If yes, than I assume the task here is to port the Photos sidebar to Granite SourcesList.
Do you mean expander on the right and bold text by the "same style as we see in Files, Music, or Geary". If yes, than I assume the task here is to port the Photos sidebar to Granite SourcesList.