create animated backgrounds // tutorial analysis

1. new solid layer, generate checkerboard pattern under effect
2. open scale, unlink x and y and scrub all the way to right
3. set opacity to 21%
4. open effects controls panel and set the anchor to -1, 0
5. set width to 25
6. add an anchor keyframe at beginning and keyframe to the end and set anchor to -1, 200

https://helpx.adobe.com/uk/after-effects/how-to/create-animated-background.html?red=a