Android : how to set dropdown arrow in spinner with background?

I have dropdown with black Background, blue outline of spinner, How to put arrow image in dropdown?

I am using

android:background="@android:drawable/btn_dropdown"

but that will remove my current background i.e. black background with blue outline. For that I am using a drawable

<shape
xmlns:android="http://schemas.android.com/apk/res/android"
android:shape= "rectangle"  >
    <solid android:color="#000000"/>
    <stroke android:width="2dp"  android:color="#405999"/>
</shape>