This demo uses the jQuery Library’s “draggable” function to make the circles movable around the screen using the mouse. (Draggable requires both jQuery and the jQuery UI libraries.) In addition, the circles have the “backdrop-filter” style set to blur and saturate, respectively, which alter the appearance of the underlying polkadots. Other filters include brightness, contrast, grayscale, hue-rotate, invert, opacity, sepia, and drop-shadow. See also the Demo Site’s JavaScript Demo page.