[filebrowser] making drag and drop area absolute because we cannot drop a file in left assit going through fb

apps/filebrowser/src/filebrowser/static/filebrowser/less/listdir_components.less

@@ -156,7 +156,7 @@
   height: 100%;
   left: 0;
   opacity: .5;
-  position: fixed;
+  position: absolute;
   width: 100%;
   top:0;
   z-index: 10000;