Web Demo: CSS Dynamic Point Light Source / Parallax Shadows
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This demonstrates a high-performance method of rendering dynamic CSS drop shadows from a simulated point light source.

The note and sun light source elements have been made interactively user-draggable by the inclusion of an external draggability package.

Until I have this documented, you can see the code on Codepen at https://codepen.io/kupietz/pen/LEpzJgL.