diff --git a/src/org/thoughtcrime/securesms/ApplicationContext.java b/src/org/thoughtcrime/securesms/ApplicationContext.java
index 3e4ea39fcb..685894dcd9 100644
--- a/src/org/thoughtcrime/securesms/ApplicationContext.java
+++ b/src/org/thoughtcrime/securesms/ApplicationContext.java
@@ -72,6 +72,7 @@ import org.thoughtcrime.securesms.loki.protocol.ClosedGroupsProtocol;
 import org.thoughtcrime.securesms.loki.protocol.SessionRequestMessageSendJob;
 import org.thoughtcrime.securesms.loki.protocol.SessionResetImplementation;
 import org.thoughtcrime.securesms.loki.utilities.Broadcaster;
+import org.thoughtcrime.securesms.loki.utilities.UiModeUtilities;
 import org.thoughtcrime.securesms.notifications.DefaultMessageNotifier;
 import org.thoughtcrime.securesms.notifications.MessageNotifier;
 import org.thoughtcrime.securesms.notifications.NotificationChannels;
@@ -215,6 +216,8 @@ public class ApplicationContext extends MultiDexApplication implements Dependenc
     publicChatManager = new PublicChatManager(this);
     updateOpenGroupProfilePicturesIfNeeded();
     registerForFCMIfNeeded(false);
+    // Set application UI mode (day/night theme) to the user selected one.
+    UiModeUtilities.setupUiModeToUserSelected(this);
     // ========
     initializeJobManager();
     initializeMessageRetrieval();
diff --git a/src/org/thoughtcrime/securesms/loki/activities/SettingsActivity.kt b/src/org/thoughtcrime/securesms/loki/activities/SettingsActivity.kt
index c6ff62f814..dc2d75345c 100644
--- a/src/org/thoughtcrime/securesms/loki/activities/SettingsActivity.kt
+++ b/src/org/thoughtcrime/securesms/loki/activities/SettingsActivity.kt
@@ -28,6 +28,7 @@ import org.thoughtcrime.securesms.avatar.AvatarSelection
 import org.thoughtcrime.securesms.crypto.ProfileKeyUtil
 import org.thoughtcrime.securesms.database.Address
 import org.thoughtcrime.securesms.database.DatabaseFactory
+import org.thoughtcrime.securesms.loki.dialogs.ChangeUiModeDialog
 import org.thoughtcrime.securesms.loki.dialogs.ClearAllDataDialog
 import org.thoughtcrime.securesms.loki.dialogs.SeedDialog
 import org.thoughtcrime.securesms.loki.utilities.fadeIn
@@ -100,11 +101,6 @@ class SettingsActivity : PassphraseRequiredActionBarActivity() {
 
     override fun onCreateOptionsMenu(menu: Menu): Boolean {
         menuInflater.inflate(R.menu.settings_general, menu)
-
-//        // Day/night themes are only available since Android 10
-//        menu.findItem(R.id.action_change_theme)
-//                .setVisible(Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q)
-
         return true
     }
 
@@ -115,15 +111,7 @@ class SettingsActivity : PassphraseRequiredActionBarActivity() {
                 true
             }
             R.id.action_change_theme -> {
-                // A temporary demo code that manually switches between day/night themes.
-                // The effect is reset after the app restart.
-                val currentUiMode = resources.configuration.uiMode and Configuration.UI_MODE_NIGHT_MASK
-                val nightMode: Int = when(currentUiMode) {
-                    Configuration.UI_MODE_NIGHT_YES -> AppCompatDelegate.MODE_NIGHT_NO
-                    else -> AppCompatDelegate.MODE_NIGHT_YES
-                }
-                AppCompatDelegate.setDefaultNightMode(nightMode)
-                recreate()
+                ChangeUiModeDialog().show(supportFragmentManager, ChangeUiModeDialog.TAG)
                 true
             }
             else -> super.onOptionsItemSelected(item)
diff --git a/src/org/thoughtcrime/securesms/loki/dialogs/ChangeUiModeDialog.kt b/src/org/thoughtcrime/securesms/loki/dialogs/ChangeUiModeDialog.kt
new file mode 100644
index 0000000000..b9e2127fd9
--- /dev/null
+++ b/src/org/thoughtcrime/securesms/loki/dialogs/ChangeUiModeDialog.kt
@@ -0,0 +1,35 @@
+package org.thoughtcrime.securesms.loki.dialogs
+
+import android.app.Dialog
+import android.os.Bundle
+import androidx.appcompat.app.AlertDialog
+import androidx.fragment.app.DialogFragment
+import org.thoughtcrime.securesms.loki.utilities.UiMode
+import org.thoughtcrime.securesms.loki.utilities.UiModeUtilities
+
+//TODO Use localized string resources.
+class ChangeUiModeDialog : DialogFragment() {
+
+    companion object {
+        public const val TAG = "ChangeUiModeDialog"
+    }
+
+    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
+        val context = requireContext()
+
+        val displayNameList = UiMode.values().map { it.displayName }.toTypedArray()
+        val activeUiMode = UiModeUtilities.getUserSelectedUiMode(context)
+
+        return AlertDialog.Builder(context)
+                .setSingleChoiceItems(displayNameList, activeUiMode.ordinal) { _, selectedItemIdx: Int ->
+                    val uiMode = UiMode.values()[selectedItemIdx]
+                    UiModeUtilities.setUserSelectedUiMode(context, uiMode)
+                    dismiss()
+                    requireActivity().recreate()
+                }
+                .setTitle("Application theme")
+                .setNegativeButton("Cancel") { _, _ -> dismiss() }
+                .create()
+
+    }
+}
\ No newline at end of file
diff --git a/src/org/thoughtcrime/securesms/loki/utilities/UiModeUtilities.kt b/src/org/thoughtcrime/securesms/loki/utilities/UiModeUtilities.kt
new file mode 100644
index 0000000000..0a24e5777a
--- /dev/null
+++ b/src/org/thoughtcrime/securesms/loki/utilities/UiModeUtilities.kt
@@ -0,0 +1,62 @@
+package org.thoughtcrime.securesms.loki.utilities
+
+import android.content.Context
+import android.content.res.Configuration
+import androidx.appcompat.app.AppCompatDelegate
+
+/**
+ * Day/night UI mode related utilities.
+ * @see <a href="https://developer.android.com/guide/topics/ui/look-and-feel/darktheme">Official Documentation</a>
+ */
+object UiModeUtilities {
+    private const val PREF_FILE_NAME = "UiModeUtilities"
+    private const val PREF_KEY_SELECTED_UI_MODE = "SELECTED_UI_MODE"
+
+    @JvmStatic
+    public fun setUserSelectedUiMode(context: Context, uiMode: UiMode) {
+        val prefs = context.getSharedPreferences(PREF_FILE_NAME, Context.MODE_PRIVATE)
+        prefs.edit()
+                .putString(PREF_KEY_SELECTED_UI_MODE, uiMode.name)
+                .apply()
+        AppCompatDelegate.setDefaultNightMode(uiMode.nightModeValue)
+    }
+
+    @JvmStatic
+    public fun getUserSelectedUiMode(context: Context): UiMode {
+        val prefs = context.getSharedPreferences(PREF_FILE_NAME, Context.MODE_PRIVATE)
+        val selectedUiModeName = prefs.getString(PREF_KEY_SELECTED_UI_MODE, UiMode.SYSTEM_DEFAULT.name)!!
+        var selectedUiMode: UiMode
+        try {
+            selectedUiMode = UiMode.valueOf(selectedUiModeName)
+        } catch (e: IllegalArgumentException) {
+            // Cannot recognize UiMode constant from the given string.
+            selectedUiMode = UiMode.SYSTEM_DEFAULT
+        }
+        return selectedUiMode
+    }
+
+    @JvmStatic
+    public fun setupUiModeToUserSelected(context: Context) {
+        val selectedUiMode = getUserSelectedUiMode(context)
+        setUserSelectedUiMode(context, selectedUiMode)
+    }
+}
+
+//TODO Use localized string resources.
+enum class UiMode(
+        val displayName: String,
+        val uiModeNightFlag: Int,
+        val nightModeValue: Int) {
+
+    DAY ("Day",
+            Configuration.UI_MODE_NIGHT_NO,
+            AppCompatDelegate.MODE_NIGHT_NO),
+
+    NIGHT ("Night",
+            Configuration.UI_MODE_NIGHT_YES,
+            AppCompatDelegate.MODE_NIGHT_YES),
+
+    SYSTEM_DEFAULT ("System default",
+            Configuration.UI_MODE_NIGHT_UNDEFINED,
+            AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM);
+}
\ No newline at end of file