function fade(node, { delay = 0, duration = 400, easing = linear } = {}) {
	const o = +getComputedStyle(node).opacity;
	return {
		delay,
		duration,
		easing,
		css: (t) => `opacity: ${t * o}`
	};
}
Animates the opacity of an element from 0 to the current opacity for `in` transitions and from the current opacity to 0 for `out` transitions.

@param {Element} node
@param {FadeParams} [params]
@returns {TransitionConfig}