title: Android Tv imageCardView background / extra content
body: <p>For Android Tv app I am using v17 leanback library and Leanback theme.</p>
  
  <p>Having problems overriding default imageCardView background color.</p>
  
  <pre><code>&lt;!-- original styles defined in Leanback theme --&gt;
  
  &lt;style name="Widget.Leanback.BaseCardViewStyle" /&gt;
  
  &lt;style name="Widget.Leanback.ImageCardViewStyle" parent="Widget.Leanback.BaseCardViewStyle"&gt;
      &lt;item name="cardType"&gt;infoUnder&lt;/item&gt;
      &lt;item name="infoVisibility"&gt;activated&lt;/item&gt;
      &lt;!-- i want to override this  --&gt;
      &lt;item name="android:background"&gt;@color/lb_basic_card_bg_color&lt;/item&gt;
  &lt;/style&gt;
  
  &lt;!-- In my styles.xml I inherit leanback theme and override imageCardViewStyle --&gt;
  &lt;style name="AppTheme" parent="Theme.Leanback"&gt;
      &lt;item name="imageCardViewStyle"&gt;@style/myImageCardViewStyle&lt;/item&gt;
  &lt;/style&gt;
  
  &lt;style name="myImageCardViewStyle"&gt;
      &lt;item name="cardType"&gt;infoUnderWithExtra&lt;/item&gt;
      &lt;item name="infoVisibility"&gt;activated&lt;/item&gt;
      &lt;item name="extraVisibility"&gt;activated&lt;/item&gt;
      &lt;!-- set new color  --&gt;
      &lt;item name="android:background"&gt;#FADCA7&lt;/item&gt;
  &lt;/style&gt;
  </code></pre>
  
  <p>Problem is that background color is always transitioned to defined "lb_basic_card_bg_color" in the Leanback theme, which I do not know how to override.</p>
  
  <p>Another thing is that I did not find the method for setting content of the imageCardView extra card region. In the API I see only setTitleText and setContentText methods.</p>