title: Android CardView with rounded corners displays grey corners
body: <p>I'm inflating a custom layout with CardView inside the layout. 
  The rounded corners are displayed as expected but I also get grey background behind the corners.</p>
  
  <p>The code is simple, uses a CardView with corner radius and a background color. 
  I've tried setting transparent background but doesn't work. However, if i set another opaque color, it is displayed in corners.</p>
  
  <p>Code is attached.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:background="@android:color/transparent"&gt;
  
      &lt;android.support.v7.widget.CardView
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          app:cardBackgroundColor="@android:color/white"
          app:cardCornerRadius="6dp"
          app:cardElevation="5dp"&gt;
  
          &lt;RelativeLayout
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:background="@android:color/transparent"&gt;
  
              &lt;TextView
                  android:id="@+id/tvProgress"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content"
                  android:layout_alignParentLeft="true"
                  android:layout_alignParentStart="true"
                  android:layout_centerVertical="true"
                  android:layout_toLeftOf="@+id/ivIcon"
                  android:layout_toStartOf="@+id/ivIcon"
                  android:background="@android:color/transparent"
                  android:padding="@dimen/elementPaddingSmall"
                  android:text="Initial Discussion"
                  android:textAppearance="?android:attr/textAppearanceMedium"
                  android:textColor="@android:color/black" /&gt;
  
              &lt;ImageView
                  android:id="@+id/ivIcon"
                  android:layout_width="50dp"
                  android:layout_height="50dp"
                  android:layout_alignParentEnd="true"
                  android:layout_alignParentRight="true"
                  android:background="@color/lightBrown"
                  android:scaleType="centerInside"
                  android:src="@drawable/ic_checkmark_circle" /&gt;
          &lt;/RelativeLayout&gt;
  
  
      &lt;/android.support.v7.widget.CardView&gt;
  &lt;/RelativeLayout&gt;
  </code></pre>
  
  <p>Result:</p>
  
  <p><a href="https://i.stack.imgur.com/FqNBa.png" rel="noreferrer"><img src="https://i.stack.imgur.com/FqNBa.png" alt="enter image description here"></a></p>