My content is in a container of 800x480 pixels. When the window resizes, my goal is to:
You can't zoom independently width and height but you can simulate the zoom effect with the CSS scale property that you can apply independently to X and Y axis :
transform: scaleX(2) scaleY(1.5);
DEMO
Don't forget to specify a transform origin to 0 0
so that the top/left of your element isn't cropped by the viewport.