function blur(
	node,
	{ delay = 0, duration = 400, easing = cubic_in_out, amount = 5, opacity = 0 } = {}
) {
	const style = getComputedStyle(node);
	const target_opacity = +style.opacity;
	const f = style.filter === 'none' ? '' : style.filter;
	const od = target_opacity * (1 - opacity);
	const [value, unit] = split_css_unit(amount);
	return {
		delay,
		duration,
		easing,
		css: (_t, u) => `opacity: ${target_opacity - od * u}; filter: ${f} blur(${u * value}${unit});`
	};
}
Animates a `blur` filter alongside an element's opacity.

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