code: function createDragConfig(container, callbackRelative) {
  
              //Convert the px coordinates to relative coordinates (0-1) before invoking the callback:
              function relayDrag(_, pos) {
                  const relX = pos[0]/container.clientWidth,
                        relY = pos[1]/container.clientHeight;
                  callbackRelative(relX, relY);
              }
  
              const config = {
                  container:     container,
                  dragOutside:   false,
                  callback:      relayDrag,
                  //Respond at once (mousedown), don't wait for click or drag:
                  callbackDragStart: relayDrag,
                  //When interacting with a picker, this allows other open picker popups to close:
                  propagateEvents: true,
              };
              return config;
          }
docs: /* Draggable color selection