In fact you can leave the ship anywhere in the game window. As long as you are not moving it, the collision detection does not work. (Anyone knows why?)
Collision detector uses CSS hover effect. If you don't move your mouse, hover is not triggered.
sigh, it just goes to show CSS/HTML alone isn't ready for such computation quite yet.
Sure hope this is sarcasm.
Actually.. There is a way to do it that I was in the process of creating for my personal CSS only game I made 2+ years ago. It involved having a div slide over the content with a specific hover event that would require the user to keep moving their mouse every X seconds or the you lose screen would cover the page.
It works in Firefox 25 for me.
Just gave it a try, you are right.
Collision detection however fails on Google Chrome 31 when the mouse pointer is not moving.
So Chrome don't recalculate :hover CSS pseudoclass when position of element changes, it does it only on mouse events.