Big margins/spacing on Linux version

[Jay2k1]

Hi,

I am using Nagstamon on both macOS and Linux. I have noticed that the layout on the mac version is more compact and dense, so I can see much more issues on my screen than I can on linux. I've made screenshots (windowed mode, default font), macOS on the left, Linux (Kubuntu) on the right:

My question is: Is there a way to reduce these margins on Linux? It wastes way too much space for my taste. I run from source anyway, so changing things in the source code is fine for me.

Thanks!