The site is using a japanese(?) font which you probably don't have and it's falling back to a serif font. If you inspect element and change it to monospace it all works fine.
Pretty cool demo. Just a little tip for op, @codez, if you apply float: right; to the menu container (.actions) the buttons will look better while sliding in/out.
Thanks very much for the feedback! and thank you very much for that little tip, haha I spent a while thinking, hmm this doesn't look right, it's funny how like when you're stuck into something you can sometimes overlook simple things that are going to fix an issue. "float: right;" palms face
Since you don't know what is in either envelope surely both theoretically contain both x and 2x (al a Schrödinger's cat). Only upon opening an envelope will we know the amount; which one you take or how many times you swap make no difference.
Also swapping, in my understanding, doesn't increase your probability. In the first choice you 1 in 2 chance of gettng the higher amount. In the second choice (the ability to swap, which is fundamentally the same as choosing between the two envelopes) you have a 1 in 2 chance of getting the higher amount.