Adds the drag over animation....

chrome/browser/resources/new_new_tab.css

 html {
   /* This is needed because of chrome://theme/css/new_tab.css */
   height: 100%;
 }
 
 body {
   margin: 0;
 }
 
 #main {
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   -webkit-border-radius: 5px;
   display: block;
   -webkit-box-shadow: 0px 2px 2px hsla(0, 0%, 0%, 0);
   -webkit-transition: width .15s, height .15s, border-color .15s,
       -webkit-border-radius .15s, -webkit-box-shadow .15s;
 }
 
 .edit-mode-border {
   -webkit-border-radius: 4px;
   background-color: hsla(213, 54%, 95%, 0);
+
+  /* when dragged over we move this */
+  position: relative;
+  -webkit-transition: top .15s, left .15s;
 }
 
 .thumbnail-container:focus .thumbnail,
 .thumbnail-container:hover .thumbnail {
   border-color: hsl(213, 66%, 57%);
   -webkit-box-shadow: 0px 2px 2px hsla(0, 0%, 0%, 0);
   -webkit-border-top-left-radius: 0;
   -webkit-border-top-right-radius: 0;
 
   background-image: -webkit-gradient(linear, left top, left bottom,
@@ skipping 451 matching lines @@
   }
 
   #t3, #t7 {
     left: 534px;
   }
 
   #t4, #t5, #t6, #t7 {
     top: 147px;
   }
 }