[Theme: Oxygen] Secondary Menu image – easy fix

I am using the Oxygen theme and I have my company logo inserted into the (black, secondary, vertical left-side) menu, attached as a “menu item image” in the menu options screen. It looks good position-wise, and serves as a primitive home button as a link.

But my problem is that as the image is sat inside the menu, the margins of the menu are affecting the logo, creating a shoddy-looking black frame around the image. Does anyone have any advice on how to either:

Shift the image up and left to overlap the existing margin; or
Cover the margins around the logo by applying some kind of white border to the image?

Any help appreciated – sorry theres no link I’m running off local server right now