suggest: move backButton to the corner?

[insulsa]

When playing on a smartphone, the screen real estate is narrow. In the meantime the backButton in the middle of the left border is annoying. I myself edited terpstr-style.css for my local copy like this:

#backButton {
    position: absolute;
    left: 0;              
    top: 0%;

This may make the backButton harder for a new user to find. However, it was already hard to find in its place as of now, in the middle of many colorful grids. I myself failed to find it for the first time, when I was using a modestly big screen. Or we can document the existence (existenthood) of it somewhere?