Canvas a bit too big?

Question

In http://onlyabutton.com/, when you press the left and right arrow keys, the window shakes a bit, most likely because of canvas dimensions. How do I fix this? Help would be appreciated!

Answer 1

You just have to add:

html, body {
    margin: 0;
}

You set the canvas width to 100% of the window size but forget to subtract the margin of body.