Its great, thanks !
however there is few problems with this technique :
1) it could lead to very small or big fonts when screen size is getting smaller or larger, so we could make some min, max to this function
2) it doesn't take into account the aspect ratio of the screen, on a lot of laptop, the users have a much wider screen than the window height, so this computation tend to deliver them a greater font, that it should.
I had to adapt it for a one-page size all project and come up with a naive implementation, that patch the size according to 4:3 aspect ratio to compensate and using a [8,24] clipping range.
so its something like :
// clip to a decent range size to avoid, making endless size adjustments as screens being bigger and bigger
var aspect_ratio = (window.innerHeight/window.innerWidth)/0.75
var vwh = window.innerWidth/100
var rem = Math.max(8,Math.min(24,vwh*aspect_ratio))
document.documentElement.style.fontSize = rem + 'px';