Cube Illusion Drag to mask/unmaks color square See the Pen <a href="https://codepen.io/firegroove/pen/bGJGgJE/1f5a982e3a2ba494591e2c8e7fe18351"> Shadow illusion</a> by Firegroove (<a href="https://codepen.io/firegroove">@firegroove</a>) on <a href="https://codepen.io">CodePen</a>.
