This is very cool and fun!

For Day 10, I don't see a snowman. I think you lose the background somewhere so it's white on white, I'm on my phone though so I can't dig in too far.

Yes, there's some bug with using gradients that I couldn't figure out yet. Are you looking at it on mobile? On desktop it works for me

I'm on Chrome for Android. I tried turning up the brightness and turning off the eye comfort shield and couldn't see it.

I took a look on my desktop and I can just barely see it. I think if you kept the blue background it would be easier on both platforms.