I am trying to add a CSS file in Magento admin section. 
Using following code in local.xml, I have added one JS file : 

```
<layout>
    <default>
        <reference name="head">
            <action method="addItem">
                 <type>skin_js</type>
                     <name>my_folder/my_js.js</name>
                 <params/>
            </action>
        </reference>
    </default>
</layout>

```

But I not able to attach a CSS file in admin section.