content.css -> content.css.erb

app/assets/stylesheets/content.css.erb

@@ -23,7 +23,7 @@ body{
 	width:100%;
 }
 #panel_header{
-	background:url(../images/bar_bg.png) repeat-x 0 0;
+	background:url(<%= asset_path 'bar_bg.png' %>) repeat-x 0 0;
 	font-size:12px;
 	height:41px;
 }
@@ -73,7 +73,7 @@ body{
 	color:#ececec;
 }
 #panel_sidebar ul{
-    background: url("../images/tree_list.png") repeat scroll 0 0 transparent;
+    background: url(<%= asset_path 'tree_list.png' %>) repeat scroll 0 0 transparent;
 }
 #panel_sidebar li{
     font-size: 12px;