#myContainer {
  position: absolute; /* Essential for movement */
  cursor: move;       /* Visual cue for the user */
  z-index: 9;
}

dragElement(document.getElementById("myContainer"));

function dragElement(elmnt) {
  let pos1 = 0, pos2 = 0, pos3 = 0, pos4 = 0;
  
  elmnt.onmousedown = dragMouseDown;

  function dragMouseDown(e) {
    e.preventDefault();
    // Get initial cursor position
    pos3 = e.clientX;
    pos4 = e.clientY;
    document.onmouseup = closeDragElement;
    document.onmousemove = elementDrag;
  }

  function elementDrag(e) {
    e.preventDefault();
    // Calculate new cursor position
    pos1 = pos3 - e.clientX;
    pos2 = pos4 - e.clientY;
    pos3 = e.clientX;
    pos4 = e.clientY;
    // Set the element's new position
    elmnt.style.top = (elmnt.offsetTop - pos2) + "px";
    elmnt.style.left = (elmnt.offsetLeft - pos1) + "px";
  }

  function closeDragElement() {
    // Stop moving when mouse button is released
    document.onmouseup = null;
    document.onmousemove = null;
  }
}