How to customise the appearance of notify-send?

I am running linux mint and use the notify-send command for various purposes, and of course also receive notifications from regular applications e.g. discord or MS Teams When using Cinnamon DE, they look pretty normal, and I can even add icons to my custom notify-send calls to make it clear what is going on However, I recently started using XMonad WM, and I'm finding that not only are the regular application notifications ugly, but my custom ones which have nice icons in them also follow that same ugly style (please excuse blurry screenshot): For example, the above notification should contain an icon as per this command: notify-send --hint=int:transient:1 'Connecting to VPN... Check 2FA Device.' -i myicon Where is this configured?