This has been fixed in Ubuntu 17.10 Alpha by updating the Ambiance and Radiance themes (LP: #1685272).
As a workaround until 17.10 is released, you could switch to a different theme like Adwaita or Numix.
This has been fixed in Ubuntu 17.10 Alpha by updating the Ambiance and Radiance themes (LP: #1685272).
As a workaround until 17.10 is released, you could switch to a different theme like Adwaita or Numix.