This could burn a little time if you're not careful.
The height/width attributes are used for the coordinate system of the canvas, while the css height/width properties are for the window itself. If the height/width attributes are not set, then they default to 300 and 150, respectively. The bottom line is that you should probably deal with these two height/width entities separately.
Here's one nice example on stackoverflow demonstrating the issue. Here's another one.