When you disable the left navigation menu, you see an menu icon at the left of the top bar. That icon has a right border that doesn't fit with the other elements in the top bar. 

Could that border be removed?

With border:
> [![With border][1]][1]

An example without border:

> [![Without border][2]][2]

  [1]: https://i.sstatic.net/eOoub.png
  [2]: https://i.sstatic.net/ubccZ.png