Took me some time to figure out that I should click slightly outside of the buttons to get the code (highlighting is barely visible on my MBP screen).
But to OP, thanks for making this. As someone who hates writing complicated CSS but loves good design, this is a great resource. I'm sure there will be haters as with most tools, but this will be useful for me.
Without hover: rgb(9, 8, 33)
With hover: rgb(13, 11, 38)¹
¹After blending. The hover actually adds rgba(24, 21, 55, .2) to the box.
The CSS trick is great, but I have to say the usage of that site is non-intuitive at all.
However, the actual effects are nice. I did notice some flashing with the "bubble" animation on Mobile Safari (probably a browser quirk). Though others like "slide" appear smooth and sleek.