[Tree] file-dropped style to highlight the folder

dist/styles/Login.css

@@ -204,6 +204,9 @@ text-align: center;
 .tree {
     margin-top: 10px;
 }
+.tree .file-dropped {
+    background-color: aliceblue;
+}
 #graph-tree .tree {
     margin-top: 27px;
 }

src/Gargantext/Components/Tree.purs

@@ -538,12 +538,14 @@ toHtml d s@(NTree (LNode {id, name, nodeType}) ary) n = R.createElement el {} []
         folderIcon folderOpen@(open /\ _) =
           H.a {onClick: R2.effToggler folderOpen}
           [ H.i {className: fldr open} [] ]
-        dropProps (_ /\ setDroppedFile) = {
-            onDrop: dropHandler
+        dropProps (droppedFile /\ setDroppedFile) = {
+            className: dropClass droppedFile
+          , onDrop: dropHandler setDroppedFile
           , onDragOver: onDragOverHandler
           }
-          where
-            dropHandler = mkEffectFn1 $ \e -> unsafePartial $ do
+        dropClass (Just _) = "file-dropped"
+        dropClass Nothing = ""
+        dropHandler setDroppedFile = mkEffectFn1 $ \e -> unsafePartial $ do
           let ff = fromJust $ item 0 $ ((e .. "dataTransfer" .. "files") :: FileList)
           liftEffect $ log2 "drop:" ff
           -- prevent redirection when file is dropped