I used the Sketch "Delicious" free UI Kit for a food recipes app. It includes 11 pixel-perfect screens. I just added Proto.io interactions and created a great prototype! This Delicious UI Kit was designed by Robert Anitei Sketch source: https://www.sketchappsources.com/free-source/1765-delicious-ui-kit-sketch-freebie-resource.html

Using variables on a slider to control the Brightness and Hue of a light bulb

Change of the header according to scroll position of content.