How do I center a logo in responsive templates?

Hi there!

I am trying to center the logo in the indigo template on the header of both the master page and the topic page. I am modifying the scss files directly, and cannot figure out where in the code to modify the position of the logo. Does anyone know? Note, I figured out how to nudge the logo left and right, but I want the image locked in the middle.

Thanks!

Stephanie