Use a class instead of id for vertical element

src/workspace-view.coffee

@@ -56,7 +56,7 @@ class WorkspaceView extends View
   @content: (state) ->
     @div id: 'workspace', tabindex: -1, =>
       @div outlet: 'horizontal', =>
-        @div id: 'vertical', outlet: 'vertical', =>
+        @div outlet: 'vertical', =>
           @div outlet: 'panes'
 
   # Private:

static/workspace-view.less

@@ -33,7 +33,7 @@ h6 {
     height: 100%;
   }
 
-  #vertical {
+  .vertical {
     display: -webkit-flex;
     -webkit-flex: 1;
     -webkit-flex-flow: column;