Form Button Label Won't Center in Button

The "Subscribe" button on this form won't stay centered vertically! I made adjustements in css and when I save, it all looks good until I refresh, then it goes wonky again as shown in the photo until I open up CSS... and so the cycle repeats.

Does anyone out there know why and how to resolve this?

https://decagon-caribou-s63f.squarespace.com/ pw:blackpanther

@tuanphan @creedon your my go-to experts around here. Anyone have advice on how to fix this? It looks fine once I go into my CSS, but as soon as I refresh the "SUBSCRIBE" word drops down...

It looks fine to me