It's a simple onload event! https://www.w3schools.com/jsref/event_onload.asp So the JS is taking the opacity from 0 to 1 once all the content of the body has loaded.
Ooh I see! Simple and yet really neat too :] I might consider using it for the transition between certain parts in my site, since I think it would be fitting
New commission page is up! Updated my prices and am offering 2 new types of commission.