Hi Stackoverflow friends. I've written `selector_button.xml` below to make my buttons more beautiful clicked. But it doesn't affect my buttons at all. Where I am wrong?

This is `selector_button.xml`

```
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" >

     <!-- When clicked  -->
    <item android:state_pressed="true"
        android:state_selected="true" >
        <shape >
        <gradient        
            android:angle="90"        
            android:centerColor="@color/Lightgray"        
            android:endColor="@color/White"        
            android:startColor="@color/LightBlue"/>    
            <corners android:radius="12dip" />    
            <stroke        
                android:width="0dip"       
                 android:color="@color/LightBlue" />

         </shape>
    </item>
    <!-- When not clicked-->
      <item >
        <shape >
        <gradient        
            android:angle="90"        
            android:centerColor="#ff008888"        
            android:endColor="@color/LightBlue"        
            android:startColor="@color/Lightgray"/>    
            <corners android:radius="12dip" />    
            <stroke        
                android:width="0dip"       
                 android:color="@color/LightBlue" />
      </shape> 
</item>

</selector>

```