Nope. Just a bunch of failures and research.
Yeah, I was a bit confused when I was making it, so I googled long shadow checkmark, and it didn't really shed much light on it. Thanks o3o
Just GIMP. I should've used inkscape (in combination with gimp), but my knowledge of how to use it is very limited.
Nice thing! and OH. MY. GOD. You're right. It isn't centred, there are six more pixels of space on the right side. I wonder how that happened. <.<
Actually, the check mark icon is from material design X'DDD