You basically can't.
Any DOM object, like html, text input, buttons, lists, etc is not rendered inside the canvas but on top of it.
That being said, if the html element is just a background element, you might be able to make your layout background transparent (all layers need to be transparent) then manually change the Z index to bring the canvas above the html object (html z-index 0 canvas z-index 1, and you'll need to add a position to the canvas (relative/absolute).
Alternatively you can set the html z-index to -1, but then you will need to set the body background to transparent.