I've seen variations on this dead-simple concept so many times I made my own two months ago: https://codepen.io/fenwick/pen/YYdXXb https://codepen.io/fenwick/p

I've seen variations on this dead-simple concept so many times I made my own two months ago: https://codepen.io/fenwick/pen/YYdXXb https://codepen.io/fenwick/pen/YYdXXb