Allow working with CSS variables instead of property values

[75th]

Of course I discover basicScroll after setting out to make my own parallax library. We'll see if I can get mine to a point where I feel Parallaxative has earned a right to exist alongside it, before giving up and just using basicScroll forever

[75th]

Found this snippet that might be useful for this later:

function vendorPrefix() {
	return (Array.prototype.slice.call(styles).join('') .match(/-(moz|webkit|ms)-/) || (styles.OLink === '' && ['', 'o']))[1];
}