logo image jumping down on mobile device

Hi guys. My site is using Catch Evolution Free theme and is on testing site here I spent ages removing white space around the logo image and finally got there last night. However when viewed on my mobile phone (or indeed when the browser is reduced to near mobile device size) the logo image jumps down by approx 10 pixels. I'm guessing it's a breakpoint. Can you tell me briefly what is causing that (for learning purposes), and then how to fix? Many thanks!