title: Trying to set spinner background white
body: <p>I am trying to set my spinner's backgroundcolour to white, and for the white spinner to sit on top of a relative layout  blue coloured box, but when I set the spinner background colour to white, the spinner disappears on the design view </p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:id="@+id/container"
      android:background="#F5F8FF"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context=".MainActivity"&gt;
  
      &lt;android.support.design.widget.BottomNavigationView
          android:id="@+id/navigation"
          android:layout_width="0dp"
          android:layout_height="wrap_content"
          android:layout_marginEnd="0dp"
          android:layout_marginStart="0dp"
          android:background="?android:attr/windowBackground"
          app:layout_constraintBottom_toBottomOf="parent"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:menu="@menu/navigation" /&gt;
  
      &lt;RelativeLayout
          android:layout_width="384dp"
          android:layout_height="65dp"
          android:layout_marginBottom="392dp"
          android:background="#23C4C4"
          app:layout_constraintBottom_toTopOf="@+id/navigation"
          app:layout_constraintEnd_toEndOf="parent"
          app:layout_constraintHorizontal_bias="0.0"
          app:layout_constraintStart_toStartOf="parent"&gt;
  
          &lt;Spinner
              android:id="@+id/spinner2"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:layout_centerVertical="true"
              android:background="#FFFFFF"/&gt;
      &lt;/RelativeLayout&gt;
  
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>