title: How to add custom item in android Theme declaration?
body: <p>I'm having few custom themes in my styles.xml <br>
  Now whenever the activity takes the theme, it uses the <strong>colorPrimary</strong>, <strong>colorPrimaryDark</strong> and <strong>colorAccent</strong> values. <br>
  For my layout's background I'm using <strong>?attr/colorAccent</strong>, so it can pick the background color based on the selected theme. <br>
  If I use any of the above values it works fine. But I want to define a custom item value for my background color.<br>
  I tried like this below but it didn't worked. any ideas to make it work ?
  <br>
  My custom theme with custom value: <br></p>
  
  <pre><code>&lt;style name = "customTheme" parent="Theme.AppCompat.Light.NoActionBar"&gt;
      &lt;item name="colorPrimary"&gt;#4285f4&lt;/item&gt;
      &lt;item name="colorPrimaryDark"&gt;#2C75F2&lt;/item&gt;
      &lt;item name="colorAccent"&gt;#E1FFC7&lt;/item&gt;
      &lt;item name="customBgColor"&gt;#d3d3d3&lt;/item&gt;
  &lt;/style&gt;
  </code></pre>
  
  <p><br>
  And I want to use it in layout's style as <br></p>
  
  <pre><code>&lt;style name="layoutStyle" &gt;
      &lt;item name="android:background"&gt;?attr/customBgColor&lt;/item&gt;
  &lt;/style&gt;
  </code></pre>