Try this
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
<item>
<shape>
<padding
android:bottom="3dip"
android:left="3dip"
android:right="3dip"
android:top="3dip" />
<corners
android:topLeftRadius="6dip"
android:topRightRadius="6dip" />
<solid android:color="#666666" />
</shape>
</item>
<item>
<shape android:shape="rectangle" >
<gradient
android:angle="270"
android:endColor="#888888"
android:startColor="#888888" />
</shape>
</item>