The existing problem is that if you had a modal window in mobile, it puts it at the top of the page and does not vertically center it, because it can't -- unles

The existing problem is that if you had a modal window in mobile, it puts it at the top of the page and does not vertically center it, because it can't -- unless the user is using ICS or something newer, or their mobile browser supports fixed positioning (which is very unlikely, see http://caniuse.com/css-fixed http://caniuse.com/css-fixed). This fix detects the standard responsive media query of 480px for mobile (which also sets `position: fixed` to `position: absolute` and adjusts accordingly.