<style name="ActivityDialog" parent="android:Theme.Holo.Light.Dialog">
  <item name="android:windowBackground">@android:color/transparent</item>
  <item name="android:windowFrame">@null</item>
  <item name="android:backgroundDimEnabled">true</item>
  <item name="android:windowIsTranslucent">true</item>
  <item name="android:windowNoTitle">true</item>
  <item name="android:windowFullscreen">true</item>
  <item name="android:windowContentOverlay">@null</item>
  <item name="android:windowAnimationStyle">@null</item>
</style>

<activity
  android:name=".MyDialogActivity"
  android:screenOrientation="portrait"
  android:theme="@style/ActivityDialog"/>