title: Can't change theme in Manifest
body: <p>Im learning, stuck at simple problem of removing Android's action bar and seting app to full screen. Whole app should be in fullscreen, so I started with Manifest </p>
  
  <pre><code>&lt;application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@android:style/Theme.Holo.Light.NoActionBar.Fullscreen"&gt;
      &lt;activity
          android:name=".Main"
          android:screenOrientation="landscape"
          android:configChanges="orientation|keyboardHidden|screenSize"
          android:label="@string/app_name"
          android:theme="@style/FullscreenTheme"&gt;
          &lt;intent-filter&gt;
              &lt;action android:name="android.intent.action.MAIN" /&gt;
  
              &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
          &lt;/intent-filter&gt;
      &lt;/activity&gt;
  &lt;/application&gt;
  </code></pre>
  
  <p>UI stays exactly the same = 
  <a href="https://i.stack.imgur.com/pntSL.png" rel="nofollow noreferrer">Stuck at default Look.</a>
  Alright next I tried changing looks in Android studio GUI for activity_main.xml screen. That changes Design preview, but no effect in actual app. Still the same. Is this meant to change app or just design preview btw?</p>
  
  <p>I tried changing in </p>
  
  <pre><code>&lt;activity
          android:name=".Main"
          android:screenOrientation="landscape"
          android:configChanges="orientation|keyboardHidden|screenSize"
          android:label="@string/app_name"
          android:theme="@style/FullscreenTheme"&gt;
          &lt;intent-filter&gt;
              &lt;action android:name="android.intent.action.MAIN" /&gt;
  
              &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
          &lt;/intent-filter&gt;
      &lt;/activity&gt;
  </code></pre>
  
  <p><code>:theme</code> to <code>@android:style/Theme.Holo.Light.NoActionBar.Fullscreen</code> but now app crashes on startup.</p>
  
  <p>I also tried making Custom theme in <code>styles.xml</code>, like this </p>
  
  <pre><code>&lt;style name="CustomMyTheme" parent="AppTheme"&gt;
      &lt;item name="android:windowFullscreen"&gt;true&lt;/item&gt;
      &lt;item name="android:windowContentOverlay"&gt;@null&lt;/item&gt;
  &lt;/style&gt;
  </code></pre>
  
  <p>But same results. I don't understand why changing theme in manifest  does not work. Is there some conflict in api version? Minimum is set to 15, 26 target and 22 emulator's version. </p>