Go in manifest file:
First set theme for all application:
<application
android:name=".MyApplication"
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" > <!--Your theme-->
...
You can set Theme for every activity
<activity
android:name=".activities.FirsActivity"
android:label="@string/title_activity_firsactivity"
android:screenOrientation="portrait"
android:theme="@android:style/Theme.Holo.Light.NoActionBar"> <!--Your theme for this activity-->
</activity>
<activity
android:name=".activities.SecondActivity"
android:label="@string/title_activity_secondactivity"
android:screenOrientation="portrait"
android:theme="@android:style/Theme.Holo.Light.NoActionBar"> <!--Your theme for this activity-->
</activity>
And go to activity.xml and on top bar ,set same theme like in manifest