…lor stop

* If the vertical component came alone, such as `at top`, then the position
  was wrongly calculated as (left, center). This is fixed.

* the radius of the canvas used was calculated as √2*(side/2). This was
  causing the painted gradient to not stretch till the end of the element
  when the gradient was positioned sufficiently off-center. The best way
  to ensure that the gradient covers the full element is having the
  radius to be √2*(longer-side) - this would ensure even gradients at the
  top-left corner to cover the bottom-right corner.