fix dragging during scrolling

zitap/static/zitap/js/mouse-drag.js

@@ -63,7 +63,7 @@ window.onload = function()
     {
       rectElement = document.createElement("div")
       rectElement.id = "rect"
-      rectElement.style.position = "absolute"
+      rectElement.style.position = "fixed"
       rectElement.style.border = "1px solid black"
       rectElement.style.zIndex = "100"
       document.body.appendChild(rectElement)