Getting a UI to be fullscreen

I saw a UI on codepen the other day that I would like to play with, does anyone know how to make it go fullscreen, I moved the divs around a bit, its working, kind of but the transition is not filling up the entire screen. what is this caused by, does anyone know how to fix it?
my attempt to make it into a fullscreen ui:

Heres the look im trying to achieve:

You made the height and width 100vh and 100vw?

Yes but it is out of proportion it gets stretched…

Using 100% or 100vx will stretch the div to fill it’s parent container. If you want a certain aspect ratio you can put the content in a div that has specific pixel height and width. Behind that, in a separate div you can put “filler” background color.