DevTools: beautify the responsive design warning message.

Source/devtools/front_end/ResponsiveDesignView.js

Index: Source/devtools/front_end/ResponsiveDesignView.js
diff --git a/Source/devtools/front_end/ResponsiveDesignView.js b/Source/devtools/front_end/ResponsiveDesignView.js
index c58c8939c4ace0500d9094f89455b962dffe0049..3e8b0618d93f1dd2f65770f761105866fffaeafb 100644
--- a/Source/devtools/front_end/ResponsiveDesignView.js
+++ b/Source/devtools/front_end/ResponsiveDesignView.js
@@ -26,8 +26,9 @@ WebInspector.ResponsiveDesignView = function(inspectedPagePlaceholder)
     this._canvas = this._canvasContainer.element.createChild("canvas", "fill");
 
     this._warningMessage = this._canvasContainer.element.createChild("div", "responsive-design-warning hidden");
+    this._warningMessage.createChild("div", "warning-icon-small");
     this._warningMessage.createChild("span");
-    var warningCloseButton = this._warningMessage.createChild("div", "responsive-design-warning-close");
+    var warningCloseButton = this._warningMessage.createChild("div", "close-button");
     warningCloseButton.addEventListener("click", this._closeOverridesWarning.bind(this), false);
     WebInspector.overridesSupport.addEventListener(WebInspector.OverridesSupport.Events.OverridesWarningUpdated, this._overridesWarningUpdated, this);