I'm trying to add a focus effect more noticeable to the FloatingActionButton of the android.support.design.

So far, I've tested to add a custom background to the button:

```
 <android.support.design.widget.FloatingActionButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/ic_done_24dp"
            android:background="@drawable/focus_gold"
            app:backgroundTint="#F7A200"
            app:pressedTranslationZ="12dp" />

```

With the drawable focus\_gold being:

```
 <?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
   <item android:state_focused="true" android:drawable="#ff9800"/>
 </selector>

```

Here is the result (the red background is normal):

unfocused: [![unfocused](https://i.stack.imgur.com/xdIKj.png)](https://i.stack.imgur.com/xdIKj.png)

focused: [![focused](https://i.stack.imgur.com/wN56i.png)](https://i.stack.imgur.com/wN56i.png)

Does anyone have an idea to set a nice and simple focus effect on a fab button with this library?

Thanks,

Vincent