diff --git a/.idea/misc.xml b/.idea/misc.xml
index e9a58ca..7b4db64 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -1,4 +1,7 @@
 <project version="4">
   <component name="ExternalStorageConfigurationManager" enabled="true" />
   <component name="ProjectRootManager" version="2" languageLevel="JDK_11" default="true" project-jdk-name="corretto-11" project-jdk-type="JavaSDK" />
+  <component name="SuppressKotlinCodeStyleNotification">
+    <option name="disableForAll" value="true" />
+  </component>
 </project>
\ No newline at end of file
diff --git a/app/release/app-release.apk b/app/release/app-release.apk
deleted file mode 100644
index 573a799..0000000
Binary files a/app/release/app-release.apk and /dev/null differ
diff --git a/app/src/main/java/org/secuso/aktivpause/activities/fragments/SettingsFragment.kt b/app/src/main/java/org/secuso/aktivpause/activities/fragments/SettingsFragment.kt
new file mode 100644
index 0000000..701eddc
--- /dev/null
+++ b/app/src/main/java/org/secuso/aktivpause/activities/fragments/SettingsFragment.kt
@@ -0,0 +1,31 @@
+/*
+ This file is part of the application Privacy Friendly Notes.
+ Privacy Friendly Notes is free software:
+ you can redistribute it and/or modify it under the terms of the
+ GNU General Public License as published by the Free Software Foundation,
+ either version 3 of the License, or any later version.
+ Privacy Friendly Notes 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 Privacy Friendly Notes. If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.secuso.aktivpause.activities.fragments;
+
+import android.os.Bundle
+import android.preference.PreferenceFragment
+import androidx.appcompat.app.AppCompatDelegate
+import org.secuso.aktivpause.R
+
+class SettingsFragment : PreferenceFragment() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        addPreferencesFromResource(R.xml.preferences)
+        findPreference("settings_day_night_theme")?.setOnPreferenceChangeListener { _, newValue ->
+            AppCompatDelegate.setDefaultNightMode(newValue.toString().toInt())
+            true;
+        }
+
+    }
+}
\ No newline at end of file
diff --git a/app/src/main/res/layout/activity_help.xml b/app/src/main/res/layout/activity_help.xml
index 55aa23d..fe3562a 100644
--- a/app/src/main/res/layout/activity_help.xml
+++ b/app/src/main/res/layout/activity_help.xml
@@ -46,6 +46,7 @@
         android:layout_height="match_parent"
         android:layout_gravity="start"
         android:fitsSystemWindows="true"
+        android:background="?attr/colorBackground"
         app:headerLayout="@layout/nav_header"
         app:menu="@menu/nav_drawer" />
 
diff --git a/app/src/main/res/layout/activity_manage_exercise_set.xml b/app/src/main/res/layout/activity_manage_exercise_set.xml
index 050a5af..40df4a6 100644
--- a/app/src/main/res/layout/activity_manage_exercise_set.xml
+++ b/app/src/main/res/layout/activity_manage_exercise_set.xml
@@ -85,6 +85,7 @@
         android:layout_height="match_parent"
         android:layout_gravity="start"
         android:fitsSystemWindows="true"
+        android:background="?attr/colorBackground"
         app:headerLayout="@layout/nav_header"
         app:menu="@menu/nav_drawer" />
 
diff --git a/app/src/main/res/layout/activity_settings.xml b/app/src/main/res/layout/activity_settings.xml
index 41235bd..fd435f0 100644
--- a/app/src/main/res/layout/activity_settings.xml
+++ b/app/src/main/res/layout/activity_settings.xml
@@ -1,81 +1,13 @@
 <?xml version="1.0" encoding="utf-8"?>
-<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:app="http://schemas.android.com/apk/res-auto"
+<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
-    android:id="@+id/drawer_layout"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:fitsSystemWindows="true"
-    tools:openDrawer="start">
-
-    <androidx.coordinatorlayout.widget.CoordinatorLayout
+    tools:context="org.secuso.aktivpause.activities.SettingsActivity">
+    <fragment
+        android:id="@+id/fragment_settings"
+        android:name="org.secuso.aktivpause.activities.fragments.SettingsFragment"
         android:layout_width="match_parent"
-        android:layout_height="match_parent"
-        tools:context="org.secuso.aktivpause.activities.EditExerciseSetActivity">
+        android:layout_height="match_parent" />
 
-        <include layout="@layout/layout_toolbar"/>
-
-        <androidx.constraintlayout.widget.ConstraintLayout
-            android:layout_width="match_parent"
-            app:layout_behavior="@string/appbar_scrolling_view_behavior"
-            android:id="@+id/main_content"
-            android:layout_height="match_parent">
-
-            <LinearLayout
-                android:orientation="horizontal"
-                android:layout_width="match_parent"
-                android:layout_height="0px"
-                android:layout_weight="1">
-
-                <LinearLayout
-                    android:id="@+id/headers"
-                    android:orientation="vertical"
-                    android:layout_width="match_parent"
-                    android:layout_height="match_parent">
-
-                    <ListView android:id="@android:id/list"
-                        android:layout_width="match_parent"
-                        android:layout_height="match_parent"
-                        android:clipToPadding="false"
-                        android:drawSelectorOnTop="false"
-                        android:cacheColorHint="@android:color/transparent"
-                        android:listPreferredItemHeight="48dp"
-                        android:scrollbarAlwaysDrawVerticalTrack="true" />
-
-                    <FrameLayout android:id="@+id/list_footer"
-                        android:layout_width="match_parent"
-                        android:layout_height="wrap_content"
-                        android:layout_weight="0" />
-
-                </LinearLayout>
-
-            </LinearLayout>
-            <LinearLayout
-                android:id="@+id/prefs_frame"
-                android:layout_width="match_parent"
-                android:layout_height="match_parent"
-                android:orientation="vertical"
-                android:visibility="visible" >
-
-                <android.preference.PreferenceFrameLayout android:id="@+id/prefs"
-                    android:layout_width="match_parent"
-                    android:layout_height="0dip"
-                    android:layout_weight="1" />
-            </LinearLayout>
-
-
-        </androidx.constraintlayout.widget.ConstraintLayout>
-
-    </androidx.coordinatorlayout.widget.CoordinatorLayout>
-
-    <com.google.android.material.navigation.NavigationView
-        android:id="@+id/nav_view"
-        tools:visibility="gone"
-        android:layout_width="wrap_content"
-        android:layout_height="match_parent"
-        android:layout_gravity="start"
-        android:fitsSystemWindows="true"
-        app:headerLayout="@layout/nav_header"
-        app:menu="@menu/nav_drawer" />
-
-</androidx.drawerlayout.widget.DrawerLayout>
\ No newline at end of file
+</RelativeLayout>
diff --git a/app/src/main/res/layout/activity_timer.xml b/app/src/main/res/layout/activity_timer.xml
index 88259b4..b192f68 100644
--- a/app/src/main/res/layout/activity_timer.xml
+++ b/app/src/main/res/layout/activity_timer.xml
@@ -323,6 +323,7 @@
         android:layout_height="match_parent"
         android:layout_gravity="start"
         android:fitsSystemWindows="true"
+        android:background="?attr/colorBackground"
         app:headerLayout="@layout/nav_header"
         app:menu="@menu/nav_drawer" />
 
diff --git a/app/src/main/res/layout/nav_header.xml b/app/src/main/res/layout/nav_header.xml
index b6b2296..02a82dc 100644
--- a/app/src/main/res/layout/nav_header.xml
+++ b/app/src/main/res/layout/nav_header.xml
@@ -2,38 +2,41 @@
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="@dimen/nav_header_height"
-    android:background="@color/colorAccent"
+    android:background="?attr/colorNavbarHeaderBackground"
     android:gravity="bottom"
     android:orientation="vertical"
     android:paddingBottom="@dimen/activity_vertical_margin"
     android:paddingTop="@dimen/activity_vertical_margin"
+    android:paddingLeft="@dimen/activity_vertical_margin"
+    android:paddingRight="@dimen/activity_vertical_margin"
     android:theme="@style/ThemeOverlay.AppCompat.Dark">
 
     <RelativeLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        android:background="#ffffff"
+        android:orientation="horizontal"
+        android:background="?attr/colorNavbarHeaderSurface"
         android:paddingTop="7dp"
-        android:paddingBottom="7dp"
-        android:orientation="horizontal">
+        android:paddingBottom="7dp">
 
         <ImageView
-            android:paddingLeft="@dimen/activity_horizontal_margin"
             android:id="@+id/imageView"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
-            android:src="@mipmap/ic_app"/>
-
+            android:paddingStart="@dimen/activity_horizontal_margin"
+            android:paddingEnd="@dimen/activity_horizontal_margin"
+            android:src="@mipmap/ic_drawer"/>
         <TextView
-            android:layout_width="match_parent"
+            android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:paddingLeft="@dimen/activity_horizontal_margin"
-            android:text="@string/app_name_short"
-            android:textColor="@color/colorPrimary"
-            android:textSize="18sp"
+            android:text="@string/app_name"
             android:textAppearance="@style/TextAppearance.AppCompat.Body1"
             android:layout_centerVertical="true"
-            android:layout_toEndOf="@+id/imageView" />
+            android:layout_toEndOf="@id/imageView"
+            android:layout_toRightOf="@id/imageView"
+            android:textColor="?attr/colorNavbarHeaderText"
+            android:textSize="18sp"/>
 
     </RelativeLayout>
 
diff --git a/app/src/main/res/values-de/strings.xml b/app/src/main/res/values-de/strings.xml
index 1f79287..43f72fb 100644
--- a/app/src/main/res/values-de/strings.xml
+++ b/app/src/main/res/values-de/strings.xml
@@ -177,4 +177,12 @@
     <string name="dialog_evaluation_yes">Ja</string>
     <string name="menu_display_evaluation_dialog">Online-Befragung</string>
 
+    <string name="settings_appearance_heading">Darstellung</string>
+    <string-array name="array_day_night_theme">
+        <item>System</item>
+        <item>Hell</item>
+        <item>Dunkel</item>
+    </string-array>
+    <string name="select_day_night_theme">Aussehen</string>
+
 </resources>
\ No newline at end of file
diff --git a/app/src/main/res/values-night/styles.xml b/app/src/main/res/values-night/styles.xml
new file mode 100644
index 0000000..fa0ab2c
--- /dev/null
+++ b/app/src/main/res/values-night/styles.xml
@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <style name="AppTheme" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
+        <item name="colorPrimary">@color/colorPrimary</item>
+        <item name="colorOnPrimary">@color/white</item>
+        <item name="colorAccent">@color/colorAccent</item>
+        <item name="colorSurface">@color/colorSurfaceDark</item>
+        <item name="colorOnSurface">@color/white</item>
+        <item name="colorSurfaceSecondary">@color/colorSurfaceSecondaryDark</item>
+        <item name="colorBackground">@color/colorBackgroundDark</item>
+        <item name="colorOnBackground">@color/white</item>
+        <item name="android:windowBackground">@color/colorBackgroundDark</item>
+
+        <item name="colorNavbarHeaderBackground">@color/colorPrimaryDark</item>
+        <item name="colorNavbarHeaderSurface">#476885</item>
+        <item name="colorNavbarHeaderText">@color/white</item>
+
+        <item name="colorIconFill">@color/white</item>
+
+    </style>
+
+    <style name="AppTheme.PopupOverlay.DialogAlert" parent="Theme.MaterialComponents.DayNight.Dialog.Alert">
+        <item name="colorPrimary">?attr/colorOnSurface</item>
+    </style>
+    <style name="AppTheme.PopupOverlay.Calendar" parent="ThemeOverlay.MaterialComponents.MaterialCalendar">
+        <item name="buttonBarButtonStyle">@style/AppTheme.PopupOverlay.Button</item>
+    </style>
+    <style name="AppTheme.PopupOverlay.Button" parent="ThemeOverlay.MaterialComponents.MaterialAlertDialog">
+        <item name="android:textColor">?attr/colorOnSurface</item>
+    </style>
+
+</resources>
\ No newline at end of file
diff --git a/app/src/main/res/values/arrays.xml b/app/src/main/res/values/arrays.xml
index cc2a7f0..764fdaf 100644
--- a/app/src/main/res/values/arrays.xml
+++ b/app/src/main/res/values/arrays.xml
@@ -18,4 +18,9 @@
         <item>Sa</item>
         <item>So</item>
     </string-array>
+    <string-array name="array_day_night_theme_values">
+        <item>-1</item>
+        <item>1</item>
+        <item>2</item>
+    </string-array>
 </resources>
\ No newline at end of file
diff --git a/app/src/main/res/values/attrs.xml b/app/src/main/res/values/attrs.xml
index b5bf108..cb0f108 100644
--- a/app/src/main/res/values/attrs.xml
+++ b/app/src/main/res/values/attrs.xml
@@ -8,4 +8,12 @@
         <attr name="layout_breakLine" format="boolean" />
         <attr name="layout_horizontalSpacing" format="dimension" />
     </declare-styleable>
+    <declare-styleable name="AppTheme">
+        <attr name="colorSurfaceSecondary" format="color" />
+        <attr name="colorBackground" format="color" />
+        <attr name="colorNavbarHeaderBackground" format="color" />
+        <attr name="colorNavbarHeaderSurface" format="color" />
+        <attr name="colorNavbarHeaderText" format="color"/>
+        <attr name="colorIconFill" format="color" />
+    </declare-styleable>
 </resources>
diff --git a/app/src/main/res/values/colors.xml b/app/src/main/res/values/colors.xml
index e05cce4..ab21b4c 100644
--- a/app/src/main/res/values/colors.xml
+++ b/app/src/main/res/values/colors.xml
@@ -2,18 +2,25 @@
 <resources>
     <color name="colorPrimary">#024265</color>
     <color name="colorPrimaryDark">#024265</color>
-    <color name="colorAccent">#0274B2</color>
+    <color name="colorSurface">#FFFFFF</color>
+    <color name="colorSurfaceDark">#373a3d</color>
+    <color name="colorBackground">#FFFFFF</color>
+    <color name="colorBackgroundDark">#050a0f</color>
+    <color name="colorSurfaceSecondary">#FFFFFF</color>
+    <color name="colorSurfaceSecondaryDark">#222222</color>
     <color name="colorLightAccent">#8aa5ce</color>
+    <color name="colorAccent">#0274B2</color>
     <color name="transparent">#00000000</color>
-    <color name="white">#ffffff</color>
-    <color name="black">#000000</color>
-    <color name="lightblue">#0274B2</color>
-    <color name="middleblue">#8aa5ce</color>
-    <color name="darkblue">#024265</color>
     <color name="middlegrey">#A8A8A8</color>
+    <color name="white">#ffffff</color>
     <color name="yellow">#f6d126</color>
+    <color name="black">#000000</color>
+    <color name="middleblue">#8aa5ce</color>
+    <color name="lightblue">#0274B2</color>
+    <color name="darkblue">#024265</color>
     <color name="red">#B71C1C</color>
     <color name="green">#388E3C</color>
+
     <color name="KITgreen">#008C84</color>
     <color name="aktivpauseGreen">#00d67d</color>
     <color name="KITlightgreen">#3BAAA2</color>
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index d8f2d44..fb08ce4 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -169,5 +169,12 @@
     <string name="dialog_evaluation_yes">Yes</string>
     <string name="menu_display_evaluation_dialog">Online Evaluation</string>
 
+    <string name="settings_appearance_heading">Appearance</string>
+    <string-array name="array_day_night_theme">
+        <item>System</item>
+        <item>Light</item>
+        <item>Dark</item>
+    </string-array>
+    <string name="select_day_night_theme">Design</string>
 
 </resources>
diff --git a/app/src/main/res/xml/pref_exercise.xml b/app/src/main/res/xml/pref_exercise.xml
deleted file mode 100644
index ebc6b29..0000000
--- a/app/src/main/res/xml/pref_exercise.xml
+++ /dev/null
@@ -1,35 +0,0 @@
-<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
-
-    <PreferenceCategory android:title="@string/pref_category_exercise">
-
-        <SwitchPreference
-            android:defaultValue="true"
-            android:key="pref_keep_screen_on_during_exercise"
-            android:title="@string/pref_keep_screen_on_during_exercise" />
-
-        <EditTextPreference
-            android:defaultValue="30"
-            android:inputType="number"
-            android:numeric="integer"
-            android:maxLength="2"
-            android:key="pref_exercise_time"
-            android:title="@string/pref_exercise_time"/>
-
-        <SwitchPreference
-            android:defaultValue="false"
-            android:key="pref_exercise_continuous"
-            android:title="@string/pref_exercise_continuous"
-            android:summary="@string/pref_exercise_continuous_summary"/>
-
-    </PreferenceCategory>
-
-    <PreferenceCategory android:title="@string/pref_category_default_exercise_sets">
-
-        <SwitchPreference
-            android:defaultValue="false"
-            android:key="pref_hide_default_exercise_sets"
-            android:title="@string/pref_hide_default_exercise_sets" />
-
-    </PreferenceCategory>
-
-</PreferenceScreen>
diff --git a/app/src/main/res/xml/pref_headers.xml b/app/src/main/res/xml/pref_headers.xml
deleted file mode 100644
index 26400db..0000000
--- a/app/src/main/res/xml/pref_headers.xml
+++ /dev/null
@@ -1,15 +0,0 @@
-<preference-headers xmlns:android="http://schemas.android.com/apk/res/android">
-
-    <!-- These settings headers are only used on tablets. -->
-
-    <header
-        android:fragment="org.secuso.aktivpause.activities.SettingsActivity$ExercisePreferenceFragment"
-        android:icon="@drawable/ic_info_black"
-        android:title="@string/pref_header_exercises" />
-
-    <header
-        android:fragment="org.secuso.aktivpause.activities.SettingsActivity$TimerSchedulePreferenceFragment"
-        android:icon="@drawable/ic_alarm_black"
-        android:title="@string/pref_header_schedule" />
-
-</preference-headers>
diff --git a/app/src/main/res/xml/pref_scheduler.xml b/app/src/main/res/xml/preferences.xml
similarity index 54%
rename from app/src/main/res/xml/pref_scheduler.xml
rename to app/src/main/res/xml/preferences.xml
index 942be8f..dda7952 100644
--- a/app/src/main/res/xml/pref_scheduler.xml
+++ b/app/src/main/res/xml/preferences.xml
@@ -1,5 +1,46 @@
 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+    <PreferenceCategory android:title="@string/settings_appearance_heading">
+        <ListPreference
+            android:key="settings_day_night_theme"
+            android:title="@string/select_day_night_theme"
+            android:summary="%s"
+            android:defaultValue="-1"
+            android:entries="@array/array_day_night_theme"
+            android:entryValues="@array/array_day_night_theme_values"
+            />
+    </PreferenceCategory>
+    <PreferenceCategory android:title="@string/pref_category_exercise">
+
+        <SwitchPreference
+            android:defaultValue="true"
+            android:key="pref_keep_screen_on_during_exercise"
+            android:title="@string/pref_keep_screen_on_during_exercise" />
+
+        <EditTextPreference
+            android:defaultValue="30"
+            android:inputType="number"
+            android:numeric="integer"
+            android:maxLength="2"
+            android:key="pref_exercise_time"
+            android:title="@string/pref_exercise_time"/>
+
+        <SwitchPreference
+            android:defaultValue="false"
+            android:key="pref_exercise_continuous"
+            android:title="@string/pref_exercise_continuous"
+            android:summary="@string/pref_exercise_continuous_summary"/>
+
+    </PreferenceCategory>
+
+    <PreferenceCategory android:title="@string/pref_category_default_exercise_sets">
+
+        <SwitchPreference
+            android:defaultValue="false"
+            android:key="pref_hide_default_exercise_sets"
+            android:title="@string/pref_hide_default_exercise_sets" />
+
+    </PreferenceCategory>
     <PreferenceCategory android:title="@string/pref_category_schedule">
 
         <SwitchPreference