The className denotes a class name (of course), and if you use fa and and corresponding fa-* class, you can select from hundreds of possible icons. Unfortunately for me, there was no "gif" icon, nor one for Tenor GIF.
So I had to set out to make my own. To do this, you'll see that above, I set the class fa-tenor-gif. This maps to nothing, since the icon doesn't exist. However, it does provide a nice easy way to find and style the button itself.
Then in my stylesheet, I simply added this styling to create my button via CSS pseudo-elements:
Fun thing about Apple Safari on iOS the bars that are not removable takes like 100px of the total height resulting in a 400px height canvas for your website and add the keyboard over this to have some fun.