How can in achieve full background smoke effect in Javascript or CSS

im trying to use this code:

http://codepen.io/MIML/pen/iBKyC

canvas {
    position:absolute;
    margin-left : 50%;
    left: -150px;
}

To put some smoke at the bottom of my page, but im searching how can i put it using 100% width!

You know, all the bottom of my page, spreads smoke.

Thanks.