respect starting opacities

Author: Rich-Harris

transition.mjs

@@ -138,13 +138,14 @@ export function crossfade({ fallback, ...defaults }) {
 
 		const style = getComputedStyle(node);
 		const transform = style.transform === 'none' ? '' : style.transform;
+		const opacity = +opacity;
 
 		return {
 			delay,
 			duration: is_function(duration) ? duration(d) : duration,
 			easing,
 			css: (t, u) => `
-				opacity: ${t};
+				opacity: ${t * opacity};
 				transform: ${transform} translate(${u * dx}px,${u * dy}px);
 			`
 		};