Device default theme (holo or material) is used for API v14 and higher .

app/src/main/AndroidManifest.xml

@@ -23,11 +23,11 @@
         android:label="@string/application_name"
         android:icon="@drawable/ic_launcher"
         android:name="com.xabber.android.data.Application"
+        android:theme="@style/Theme.Light"
         >
         <activity
             android:label="@string/application_name"
             android:name="com.xabber.android.ui.ContactList"
-            android:theme="@style/Theme.NoTitleBar"
             android:launchMode="singleTop"
             >
             <intent-filter>
@@ -64,37 +64,30 @@
         </activity>
         <activity
             android:name="com.xabber.android.ui.LoadActivity"
-            android:theme="@style/Theme.NoTitleBar"
             />
         <activity
             android:label="@string/about_viewer"
             android:name="com.xabber.android.ui.AboutViewer"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/preference_accounts"
             android:name="com.xabber.android.ui.AccountList"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/account_editor"
             android:name="com.xabber.android.ui.AccountEditor"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/chat_list"
             android:name="com.xabber.android.ui.ChatList"
-            android:theme="@android:style/Theme.Dialog"
             />
         <activity
             android:label="@string/occupant_list"
             android:name="com.xabber.android.ui.OccupantList"
-            android:theme="@android:style/Theme.Dialog"
             />
         <activity
             android:label="@string/chat_viewer"
             android:name="com.xabber.android.ui.ChatViewer"
-            android:theme="@style/Theme.Light.NoTitleBar"
             android:windowSoftInputMode="adjustResize"
             android:launchMode="singleTop"
             >
@@ -105,47 +98,38 @@
         <activity
             android:label="@string/contact_editor"
             android:name="com.xabber.android.ui.ContactEditor"
-            android:theme="@style/Theme.NoTitleBar"
             />
         <activity
             android:label="@string/contact_add"
             android:name="com.xabber.android.ui.ContactAdd"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/account_add"
             android:name="com.xabber.android.ui.AccountAdd"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/account_oauth"
             android:name="com.xabber.android.ui.OAuthActivity"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/muc_add"
             android:name="com.xabber.android.ui.MUCEditor"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/status_editor"
             android:name="com.xabber.android.ui.StatusEditor"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/preference_editor"
             android:name="com.xabber.android.ui.PreferenceEditor"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/chat_settings"
             android:name="com.xabber.android.ui.ChatEditor"
-            android:theme="@style/Theme"
             />
         <activity
             android:label="@string/contact_viewer"
             android:name="com.xabber.android.ui.ContactViewer"
-            android:theme="@style/Theme"
             android:icon="@drawable/ic_information"
             >
             <intent-filter>
@@ -159,17 +143,12 @@
         <activity
             android:name="com.xabber.android.ui.FingerprintViewer"
             android:label="@string/otr_verify_fingerprint"
-            android:theme="@style/Theme.NoTitleBar"
             />
         <activity
             android:name="com.xabber.android.ui.QuestionViewer"
             android:label="@string/otr_verify_fingerprint"
-            android:theme="@style/Theme.NoTitleBar"
-            />
-        <activity
-            android:name="com.xabber.android.ui.OpenSourceViewer"
-            android:theme="@style/Theme.NoTitleBar"
             />
+
         <activity
             android:name="com.xabber.android.ui.ContactSubscription"
             />
@@ -187,12 +166,10 @@
             />
         <activity
             android:name="com.xabber.android.ui.PhraseList"
-            android:theme="@style/Theme"
             android:label="@string/events_phrases_title"
             />
         <activity
             android:name="com.xabber.android.ui.PhraseEditor"
-            android:theme="@style/Theme"
             />
         <activity
             android:name="com.xabber.android.ui.ReconnectionActivity"
@@ -205,7 +182,6 @@
             android:noHistory="true"
             android:stateNotNeeded="true"
             android:excludeFromRecents="true"
-            android:theme="@android:style/Theme.NoDisplay"
             />
         <service android:name="com.xabber.android.service.XabberService" />
         <service

app/src/main/res/values-v14/theme.xml

+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2013, Redsolution LTD. All rights reserved.
+
+     This file is part of Xabber project; you can redistribute it and/or
+     modify it under the terms of the GNU General Public License, Version 3.
+
+     Xabber is distributed in the hope that it will be useful, but
+     WITHOUT ANY WARRANTY; without even the implied warranty of
+     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+
+     You should have received a copy of the GNU General Public License,
+     along with this program. If not, see http://www.gnu.org/licenses/.
+-->
+<resources>
+
+    <style name="Theme" parent="@android:style/Theme.DeviceDefault">
+        <item name="expanderBackground">@drawable/expander_background_dark</item>
+        <item name="expanderGroupColor">?android:attr/textColorPrimary</item>
+        <item name="expanderAccountColor">?android:attr/textColorPrimaryInverse</item>
+        <item name="expanderIndicator">@drawable/expander_indicator_dark</item>
+        <item name="accountBackground">@drawable/account_background</item>
+        <item name="titleMainBackground">@drawable/title_main_background_dark</item>
+        <item name="titleAccountBackground">@drawable/title_account_background_light</item>
+        <item name="textColorPrimaryNoSelected">@color/bright_foreground_dark</item>
+    </style>
+
+    <style name="Theme.NoTitleBar" parent="@android:style/Theme.DeviceDefault.NoActionBar">
+        <item name="expanderBackground">@drawable/expander_background_dark</item>
+        <item name="expanderGroupColor">?android:attr/textColorPrimary</item>
+        <item name="expanderAccountColor">?android:attr/textColorPrimaryInverse</item>
+        <item name="expanderIndicator">@drawable/expander_indicator_dark</item>
+        <item name="accountBackground">@drawable/account_background</item>
+        <item name="titleMainBackground">@drawable/title_main_background_dark</item>
+        <item name="titleAccountBackground">@drawable/title_account_background_light</item>
+        <item name="textColorPrimaryNoSelected">@color/bright_foreground_dark</item>
+    </style>
+
+    <style name="Theme.Dark" parent="@android:style/Theme.DeviceDefault">
+        <item name="expanderBackground">@drawable/expander_background_dark</item>
+        <item name="expanderGroupColor">?android:attr/textColorPrimary</item>
+        <item name="expanderAccountColor">?android:attr/textColorPrimaryInverse</item>
+        <item name="accountBackground">@drawable/account_background</item>
+        <item name="expanderIndicator">@drawable/expander_indicator_dark</item>
+        <item name="titleMainBackground">@drawable/title_main_background_dark</item>
+        <item name="titleAccountBackground">@drawable/title_account_background_dark</item>
+        <item name="textColorPrimaryNoSelected">@color/bright_foreground_dark</item>
+    </style>
+
+    <style name="Theme.Dark.NoTitleBar" parent="@android:style/Theme.DeviceDefault.NoActionBar">
+        <item name="expanderBackground">@drawable/expander_background_dark</item>
+        <item name="expanderGroupColor">?android:attr/textColorPrimary</item>
+        <item name="expanderAccountColor">?android:attr/textColorPrimaryInverse</item>
+        <item name="expanderIndicator">@drawable/expander_indicator_dark</item>
+        <item name="accountBackground">@drawable/account_background</item>
+        <item name="titleMainBackground">@drawable/title_main_background_dark</item>
+        <item name="titleAccountBackground">@drawable/title_account_background_dark</item>
+        <item name="textColorPrimaryNoSelected">@color/bright_foreground_dark</item>
+    </style>
+
+    <style name="Theme.Light" parent="@android:style/Theme.DeviceDefault.Light">
+        <item name="expanderBackground">@drawable/expander_background_light</item>
+        <item name="expanderGroupColor">?android:attr/textColorPrimary</item>
+        <item name="expanderAccountColor">?android:attr/textColorPrimary</item>
+        <item name="expanderIndicator">@drawable/expander_indicator_light</item>
+        <item name="accountBackground">@drawable/account_background</item>
+        <item name="titleMainBackground">@drawable/title_main_background_light</item>
+        <item name="titleAccountBackground">@drawable/title_account_background_light</item>
+        <item name="textColorPrimaryNoSelected">@color/bright_foreground_light</item>
+    </style>
+
+    <style name="Theme.Light.NoTitleBar" parent="@android:style/Theme.DeviceDefault.Light.NoActionBar">
+        <item name="expanderBackground">@drawable/expander_background_light</item>
+        <item name="expanderGroupColor">?android:attr/textColorPrimary</item>
+        <item name="expanderAccountColor">?android:attr/textColorPrimary</item>
+        <item name="expanderIndicator">@drawable/expander_indicator_light</item>
+        <item name="accountBackground">@drawable/account_background</item>
+        <item name="titleMainBackground">@drawable/title_main_background_light</item>
+        <item name="titleAccountBackground">@drawable/title_account_background_light</item>
+        <item name="textColorPrimaryNoSelected">@color/bright_foreground_light</item>
+    </style>
+
+</resources>
\ No newline at end of file