title: Android AlertDialog with AppCompat style - background issue
body: <p>Based on few websites, I applied AppCompat theme to AlertDialog.
  One issue appeared:</p>
  
  <p><a href="https://i.stack.imgur.com/1zboK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1zboK.png" alt="enter image description here"></a></p>
  
  <p>How can I remove these gray gaps ?</p>
  
  <p>My style for this AlertDialog:</p>
  
  <pre><code>&lt;style name="MyTheme.Dark.Dialog" parent="Theme.AppCompat.Dialog.Alert"&gt;
     &lt;item name="colorAccent"&gt;@color/white&lt;/item&gt;
     &lt;item name="android:colorBackground"&gt;@color/primary&lt;/item&gt;
     &lt;item name="android:windowBackground"&gt;@color/transparent&lt;/item&gt;
     &lt;item name="android:textColorPrimary"&gt;@color/iron&lt;/item&gt;
     &lt;item name="android:background"&gt;@color/primary&lt;/item&gt;
     &lt;item name="android:buttonBarButtonStyle"&gt;@style/customButtonStyle&lt;/item&gt;
     &lt;item name="android:fullDark"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:topDark"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:centerDark"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:bottomDark"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:fullBright"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:topBright"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:centerBright"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:bottomBright"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:bottomMedium"&gt;@color/red&lt;/item&gt;
     &lt;item name="android:centerMedium"&gt;@color/red&lt;/item&gt;
  &lt;/style&gt;
  
  &lt;style name="customButtonStyle" &gt;
     &lt;item name="android:textColor"&gt;@color/iron&lt;/item&gt;
     &lt;item name="android:background"&gt;@color/primary&lt;/item&gt;
  &lt;/style&gt;
  </code></pre>