Panel containers have the orientation

src/panel-container-element.coffee

@@ -11,6 +11,8 @@ class PanelContainerElement extends HTMLElement
     @subscriptions.add @model.onDidRemovePanel(@panelRemoved.bind(this))
     @subscriptions.add @model.onDidDestroy(@destroyed.bind(this))
 
+    @setAttribute('orientation', @model.getOrientation())
+
   panelAdded: ({panel, index}) ->
     if index >= @childNodes.length
       @appendChild(panel.getView())

src/panel-container.coffee

@@ -3,7 +3,7 @@
 # Public:
 module.exports =
 class PanelContainer
-  constructor: ({@viewRegistry}) ->
+  constructor: ({@viewRegistry, @orientation}) ->
     @emitter = new Emitter
     @subscriptions = new CompositeDisposable
     @panels = []
@@ -33,6 +33,8 @@ class PanelContainer
 
   getView: -> @viewRegistry.getView(this)
 
+  getOrientation: -> @orientation
+
   getPanels: -> @panels
 
   addPanel: (panel) ->