diff --git a/docs/implementation-examples.md b/docs/implementation-examples.md
new file mode 100644
index 00000000..1d2acd55
--- /dev/null
+++ b/docs/implementation-examples.md
@@ -0,0 +1,113 @@
+## Implementation examples
+
+This document functions as a dev journal, documenting some changes made and
+the corresponding code modifications.  
+It may serve as an inspiration for future feature implementation and bug
+fixes. Especially for those that are not familiar with the project code, but I will be using
+it as a cheatsheet all the time as well probably.
+
+### Adding a simple new field `theme`
+
+The user can choose a theme that should be saved in the database.  
+There are a few places where the code has to be modified and the field added
+so that it works like expected.  
+The value can only be added by **update**, so we only need to
+change one action.  
+#### Recap
+* `UserTheme.php` create theme enum. 
+* `UserSubmitUpdateAction.php` add argument to `malformedRequestBodyChecker()` call.
+* `UserValidator.php` add validation line in `validateUserUpdate()`.
+* `UserAuthorizationChecker.php` add to the `$grantedUpdateKeys` in `isGrantedToUpdate()`.
+* `UserUpdater.php` add to the `if(in_array())` in `updateUser()`.
+* `UserData.php` add to the instance variables and constructor.
+* `UserFinderRepository.php` add to the instance variable `$fields`.
+* `UserUpdateProvider.php` add theme change to `$basicDataChanges` var in `userUpdateAuthorizationCases()`.
+* `UserUpdateProvider.php` add theme change to request body and error message to response 
+in `invalidUserUpdateCases()`.
+
+#### Implementation
+
+* The field is stored as enum in the database, and it is possible that one day there
+will be other themes than just light and dark, so it makes sense to create a php enum:
+    ```php
+    // Domain/User/Enum/UserTheme.php
+    enum UserTheme: string
+    {
+        case light = 'light';
+        case dark = 'dark';
+    }
+    ```
+* In the action class `UserSubmitUpdateAction.php`, `'theme'` has to be added to the
+  `malformedRequestBodyChecker` argument list, so it knows `theme` is an accepted value.
+* After it passed the request body keys validator, the service function `updateUser()`
+is called which first validates the values `validateUserUpdate()`. As it's a backed enum
+the function `validateBackedEnum()` can be used:
+    ```php
+  // UserValidator.php validateUserUpdate()  
+  // ...
+  if (array_key_exists('theme', $userValues)) {
+        $this->validator->validateBackedEnum(
+            $userValues['theme'],
+            UserTheme::class,
+            'theme',
+            $validationResult
+        );
+    }
+    ```
+* When value validation is done, authorization is tested with `isGrantedToUpdate()`. 
+It checks if authenticated user is allowed to change given field. The way it works
+is by adding the field name to a `$grantedUpdateKeys` array if the permissions match.  
+`theme` has the same authorization rules as the other "general user data" so it's added 
+right below the list:
+    ```php
+    if (array_key_exists('theme', $userDataToUpdate)) {
+        $grantedUpdateKeys[] = 'theme';
+    }
+    ```
+* The service function `updateUser()` creates an array of the fields that may be updated
+to be certain that only the fields that are designed to be updated actually get changed:
+    ```php
+    if (in_array($column, ['first_name', '...', 'theme'], true)) {
+        $validUpdateData[$column] = $value;
+    }
+    ```
+* Now to be able to read this value and so the app knows that `theme` is now a user value, 
+add it to `UserData.php` instance variables and also the constructor.
+    ```php
+    class UserData implements \JsonSerializable
+    {
+        /* ... */    
+        public ?UserTheme $theme = null;
+    
+        public function __construct(array $userData = [])
+        {
+            $this->theme = $userData['theme'] ?? null ? UserTheme::tryFrom($userData['theme']) : null;
+        }
+    }
+    ```
+* The file that retrieves the user values from the database is the repository `UserFinderRepository.php`
+and it retrieves only the requested values, not automatically all fields. The list of values that
+should be selected are in an instance variable of this file `$fields`: 
+    ```php
+    class UserFinderRepository
+    {
+        private array $fields = ['id', '...', 'theme',];
+        // ...
+    }
+    ```
+#### Testing
+* User theme value is an extremely simple, value therefore not much has to be done especially when
+there are good existing tests.  
+The test itself doesn't even has to be changed, only the data provider that feeds it values
+`UserUpdateProvider.php`:
+  ```php
+  public static function userUpdateAuthorizationCases(): array
+  {
+      // ...
+      $basicDataChanges = ['first_name' => 'NewFirstName', '...', 'theme' => 'dark'];
+      // ...
+  }
+  ```
+* There is a validation being made so an invalid value should be tested as well. For this the function  
+`invalidUserUpdateCases()` can be extended to also include `'theme' => 'invalid',` in the request body
+and `['field' => 'theme', 'message' => 'theme not existing'],` in the response validation errors.
\ No newline at end of file
diff --git a/public/assets/general/ajax/submit-update-data.js b/public/assets/general/ajax/submit-update-data.js
index f7da03f0..2f3226e8 100644
--- a/public/assets/general/ajax/submit-update-data.js
+++ b/public/assets/general/ajax/submit-update-data.js
@@ -8,7 +8,7 @@ import {handleFail, removeValidationErrorMessages} from "./ajax-util/fail-handle
  * On success validation errors are removed and response content returned
  *
  * @param {object} formFieldsAndValues {field: value} e.g. {[input.name]: input.value}
- * @param {string} route after base path
+ * @param {string} route after base path e.g. clients/1
  * @param {boolean|string} redirectToRouteIfUnauthenticated true or redirect route url after base path.
  * If true, the redirect url is the same as the given route
  *
diff --git a/public/assets/general/dark-mode/dark-mode.js b/public/assets/general/dark-mode/dark-mode.js
index 89858cac..324152c1 100644
--- a/public/assets/general/dark-mode/dark-mode.js
+++ b/public/assets/general/dark-mode/dark-mode.js
@@ -1,4 +1,7 @@
 // Get the toggle switch element
+import {submitUpdate} from "../ajax/submit-update-data.js?v=0.2.1";
+import {displayFlashMessage} from "../page-component/flash-message/flash-message.js?v=0.2.1";
+
 const toggleSwitch = document.querySelector('#dark-mode-toggle-checkbox');
 
 // Retrieve the current theme from localStorage
@@ -6,7 +9,7 @@ const currentTheme = localStorage.getItem('theme') ? localStorage.getItem('theme
 
 // Set the theme based on the stored value from localStorage
 if (currentTheme) {
-    // Set the data-theme attribute on the root element
+    // Set the data-theme attribute on the html element
     document.documentElement.setAttribute('data-theme', currentTheme);
 
     // Check the toggle switch if the current theme is 'dark'
@@ -18,31 +21,30 @@ if (currentTheme) {
 // Add event listener to the toggle switch for theme switching
 toggleSwitch.addEventListener('change', switchTheme, false);
 
-// Set the theme on initial load if there is a stored value in localStorage
-if (currentTheme) {
-    // Set the data-theme attribute on the root element
-    document.documentElement.setAttribute('data-theme', currentTheme);
-
-    // If the current theme is 'dark', set the data-theme attribute to 'dark'
-    if (currentTheme === 'dark') {
-        document.documentElement.setAttribute('data-theme', 'dark');
-    }
-}
-
 /**
  * Handle theme switching with localstorage
  *
  * @param e
  */
 function switchTheme(e) {
+    let theme;
     // Check the current theme and switch to the opposite theme
     if (document.documentElement.getAttribute('data-theme') === 'dark') {
-        document.documentElement.setAttribute('data-theme', 'light');
-        localStorage.setItem('theme', 'light');
+        theme = 'light';
     } else {
-        document.documentElement.setAttribute('data-theme', 'dark');
-        localStorage.setItem('theme', 'dark');
+        theme = 'dark';
     }
+    // Set html data-attribute and local storage entry
+    document.documentElement.setAttribute('data-theme', theme);
+    localStorage.setItem('theme', theme);
+
+    // Make ajax call to change value in database
+    let userId = document.getElementById('user-id').value;
+    submitUpdate({theme: theme}, `users/${userId}`, true)
+        .then(r => {})
+        .catch(r => {
+            displayFlashMessage('error', 'Failed to change the theme in the database.')
+        });
 }
 
 
diff --git a/public/assets/general/page-component/flash-message/flash-message.css b/public/assets/general/page-component/flash-message/flash-message.css
index 7c9eb592..d4f28b35 100644
--- a/public/assets/general/page-component/flash-message/flash-message.css
+++ b/public/assets/general/page-component/flash-message/flash-message.css
@@ -177,6 +177,10 @@
         /*width: 200px;*/
         /*display: block;*/
     }
+    .flash-message a{
+        color: black;
+        font-weight: bold;
+    }
 
     .flash-close-btn {
         position: absolute;
diff --git a/public/assets/user/read/user-update-contenteditable.js b/public/assets/user/read/user-update-contenteditable.js
index 9df0e043..63c9f317 100644
--- a/public/assets/user/read/user-update-contenteditable.js
+++ b/public/assets/user/read/user-update-contenteditable.js
@@ -48,7 +48,7 @@ function saveUserValueAndDisableContentEditable(field) {
     submitUpdate(
         {[field.dataset.name]: field.textContent.trim()},
         `users/${userId}`,
-        `users/${userId}`
+        true
     ).then(responseJson => {
         // Field disabled before save request and re enabled on error
     }).catch(responseJson => {
diff --git a/resources/migrations/20230606142721_db_change_1316013665647f_42494524b.php b/resources/migrations/20230606142721_db_change_1316013665647f_42494524b.php
new file mode 100644
index 00000000..e5af1c60
--- /dev/null
+++ b/resources/migrations/20230606142721_db_change_1316013665647f_42494524b.php
@@ -0,0 +1,40 @@
+<?php
+
+class DbChange1316013665647f42494524b extends Phinx\Migration\AbstractMigration
+{
+    public function change()
+    {
+        $this->table('user', [
+                'id' => false,
+                'primary_key' => ['id'],
+                'engine' => 'InnoDB',
+                'encoding' => 'utf8mb4',
+                'collation' => 'utf8mb4_unicode_ci',
+                'comment' => '',
+                'row_format' => 'DYNAMIC',
+            ])
+            ->addColumn('theme', 'enum', [
+                'null' => true,
+                'default' => 'light',
+                'limit' => 5,
+                'values' => ['light', 'dark'],
+                'after' => 'password_hash',
+            ])
+            ->changeColumn('updated_at', 'datetime', [
+                'null' => true,
+                'default' => 'CURRENT_TIMESTAMP',
+                'after' => 'theme',
+            ])
+            ->changeColumn('created_at', 'datetime', [
+                'null' => true,
+                'default' => 'CURRENT_TIMESTAMP',
+                'after' => 'updated_at',
+            ])
+            ->changeColumn('deleted_at', 'datetime', [
+                'null' => true,
+                'default' => null,
+                'after' => 'created_at',
+            ])
+            ->save();
+    }
+}
diff --git a/resources/schema/schema.php b/resources/schema/schema.php
index e113dbc0..39074b23 100644
--- a/resources/schema/schema.php
+++ b/resources/schema/schema.php
@@ -1602,12 +1602,36 @@
           'IS_GENERATED' => 'NEVER',
           'GENERATION_EXPRESSION' => NULL,
         ),
+        'theme' => 
+        array (
+          'TABLE_CATALOG' => 'def',
+          'TABLE_NAME' => 'user',
+          'COLUMN_NAME' => 'theme',
+          'ORDINAL_POSITION' => 8,
+          'COLUMN_DEFAULT' => '\'light\'',
+          'IS_NULLABLE' => 'YES',
+          'DATA_TYPE' => 'enum',
+          'CHARACTER_MAXIMUM_LENGTH' => 5,
+          'CHARACTER_OCTET_LENGTH' => 20,
+          'NUMERIC_PRECISION' => NULL,
+          'NUMERIC_SCALE' => NULL,
+          'DATETIME_PRECISION' => NULL,
+          'CHARACTER_SET_NAME' => 'utf8mb4',
+          'COLLATION_NAME' => 'utf8mb4_unicode_ci',
+          'COLUMN_TYPE' => 'enum(\'light\',\'dark\')',
+          'COLUMN_KEY' => '',
+          'EXTRA' => '',
+          'PRIVILEGES' => 'select,insert,update,references',
+          'COLUMN_COMMENT' => '',
+          'IS_GENERATED' => 'NEVER',
+          'GENERATION_EXPRESSION' => NULL,
+        ),
         'updated_at' => 
         array (
           'TABLE_CATALOG' => 'def',
           'TABLE_NAME' => 'user',
           'COLUMN_NAME' => 'updated_at',
-          'ORDINAL_POSITION' => 8,
+          'ORDINAL_POSITION' => 9,
           'COLUMN_DEFAULT' => 'current_timestamp()',
           'IS_NULLABLE' => 'YES',
           'DATA_TYPE' => 'datetime',
@@ -1631,7 +1655,7 @@
           'TABLE_CATALOG' => 'def',
           'TABLE_NAME' => 'user',
           'COLUMN_NAME' => 'created_at',
-          'ORDINAL_POSITION' => 9,
+          'ORDINAL_POSITION' => 10,
           'COLUMN_DEFAULT' => 'current_timestamp()',
           'IS_NULLABLE' => 'YES',
           'DATA_TYPE' => 'datetime',
@@ -1655,7 +1679,7 @@
           'TABLE_CATALOG' => 'def',
           'TABLE_NAME' => 'user',
           'COLUMN_NAME' => 'deleted_at',
-          'ORDINAL_POSITION' => 10,
+          'ORDINAL_POSITION' => 11,
           'COLUMN_DEFAULT' => 'NULL',
           'IS_NULLABLE' => 'YES',
           'DATA_TYPE' => 'datetime',
diff --git a/resources/schema/schema.sql b/resources/schema/schema.sql
index 1011f981..a99064a0 100644
--- a/resources/schema/schema.sql
+++ b/resources/schema/schema.sql
@@ -70,6 +70,7 @@ CREATE TABLE `user` (
   `status` enum('active','locked','unverified','suspended') DEFAULT 'unverified',
   `email` varchar(254) NOT NULL,
   `password_hash` varchar(300) NOT NULL,
+  `theme` enum('light','dark') DEFAULT 'light',
   `updated_at` datetime DEFAULT current_timestamp(),
   `created_at` datetime DEFAULT current_timestamp(),
   `deleted_at` datetime DEFAULT NULL,
diff --git a/src/Application/Actions/Authentication/Submit/LoginSubmitAction.php b/src/Application/Actions/Authentication/Submit/LoginSubmitAction.php
index 401c1101..deb11457 100644
--- a/src/Application/Actions/Authentication/Submit/LoginSubmitAction.php
+++ b/src/Application/Actions/Authentication/Submit/LoginSubmitAction.php
@@ -9,6 +9,7 @@
 use App\Domain\Authentication\Service\LoginVerifier;
 use App\Domain\Factory\LoggerFactory;
 use App\Domain\Security\Exception\SecurityException;
+use App\Domain\User\Service\UserFinder;
 use App\Domain\Validation\ValidationException;
 use Odan\Session\SessionInterface;
 use Psr\Http\Message\ResponseInterface as Response;
@@ -26,6 +27,7 @@ public function __construct(
         private readonly LoginVerifier $loginVerifier,
         private readonly SessionInterface $session,
         private readonly MalformedRequestBodyChecker $malformedRequestBodyChecker,
+        private readonly UserFinder $userFinder,
     ) {
         $this->logger = $logger->addFileHandler('error.log')->createInstance('auth-login');
     }
@@ -57,12 +59,22 @@ public function __invoke(ServerRequest $request, Response $response): Response
                 // Add success message to flash
                 $flash->add('success', 'Login successful');
 
+                // Check if user has enabled dark mode and if yes populate var
+                $themeQueryParams = [];
+                if ($theme = $this->userFinder->findUserById($userId)->theme) {
+                    $themeQueryParams['theme'] = $theme->value;
+                }
+
                 // After register and login success, check if user should be redirected
                 if (isset($queryParams['redirect'])) {
-                    return $this->responder->redirectToUrl($response, $request->getQueryParams()['redirect']);
+                    return $this->responder->redirectToUrl(
+                        $response,
+                        $request->getQueryParams()['redirect'],
+                        $themeQueryParams
+                    );
                 }
 
-                return $this->responder->redirectToRouteName($response, 'home-page');
+                return $this->responder->redirectToRouteName($response, 'home-page', [], $themeQueryParams);
             } catch (ValidationException $ve) {
                 return $this->responder->renderOnValidationError(
                     $response,
diff --git a/src/Application/Actions/User/Ajax/UserSubmitUpdateAction.php b/src/Application/Actions/User/Ajax/UserSubmitUpdateAction.php
index d6a29db5..720865be 100644
--- a/src/Application/Actions/User/Ajax/UserSubmitUpdateAction.php
+++ b/src/Application/Actions/User/Ajax/UserSubmitUpdateAction.php
@@ -60,6 +60,9 @@ public function __invoke(
             'email',
             'status',
             'user_role_id',
+            'theme',
+            // When adding a new field also add it in updateUser(), validateUserUpdate(), isGrantedToUpdate(),
+            // UserFinderRepository->fields and don't forget testing
         ])) {
             try {
                 $updated = $this->userUpdater->updateUser($userIdToChange, $userValuesToChange);
diff --git a/src/Application/Middleware/PhpViewExtensionMiddleware.php b/src/Application/Middleware/PhpViewExtensionMiddleware.php
index 351737ed..1d79f807 100644
--- a/src/Application/Middleware/PhpViewExtensionMiddleware.php
+++ b/src/Application/Middleware/PhpViewExtensionMiddleware.php
@@ -44,11 +44,11 @@ public function process(
             'uri' => $request->getUri(),
             'basePath' => $this->app->getBasePath(),
             'route' => $this->app->getRouteCollector()->getRouteParser(),
-            'currRouteName' => RouteContext::fromRequest($request)->getRoute()->getName(),
+            'currRouteName' => RouteContext::fromRequest($request)->getRoute()?->getName(),
             'flash' => $this->session->getFlash(),
             // Used for public values used by view like company email address
             'config' => $this->publicSettings,
-            // Check if granted to read user that is different from the logged in one (+1)
+            // Check if granted to read user that is different then the authenticated user itself (+1)
             'userListAuthorization' => $this->userAuthorizationChecker->isGrantedToRead(
                 ($this->session->get('user_id') ?? 1) + 1
             ),
diff --git a/src/Domain/User/Authorization/UserAuthorizationChecker.php b/src/Domain/User/Authorization/UserAuthorizationChecker.php
index ed3ff1b3..52bdd98e 100644
--- a/src/Domain/User/Authorization/UserAuthorizationChecker.php
+++ b/src/Domain/User/Authorization/UserAuthorizationChecker.php
@@ -177,6 +177,11 @@ public function isGrantedToUpdate(
                 if (array_key_exists('password_hash', $userDataToUpdate)) {
                     $grantedUpdateKeys[] = 'password_hash';
                 }
+                if (array_key_exists('theme', $userDataToUpdate)) {
+                    $grantedUpdateKeys[] = 'theme';
+                }
+                // If new basic data fiel is added, add it to provider userUpdateAuthorizationCases() $basicDataChanges
+                // and invalid value to provider invalidUserUpdateCases()
 
                 // Things that only managing_advisor and higher privileged are allowed to do with users (and not if own profile)
                 // If user is managing advisor we know by the parent if-statement that the user to change has not higher
diff --git a/src/Domain/User/Data/UserData.php b/src/Domain/User/Data/UserData.php
index f45351da..5da71af4 100644
--- a/src/Domain/User/Data/UserData.php
+++ b/src/Domain/User/Data/UserData.php
@@ -3,6 +3,7 @@
 namespace App\Domain\User\Data;
 
 use App\Domain\User\Enum\UserStatus;
+use App\Domain\User\Enum\UserTheme;
 
 /**
  * Class User also serving as DTO for simplicity reasons. More details on slim-api-example/issues/2
@@ -21,6 +22,7 @@ class UserData implements \JsonSerializable
     public ?string $password2;
     public ?string $passwordHash;
     public ?UserStatus $status = null;
+    public ?UserTheme $theme = null;
     public ?int $userRoleId = null;
     public ?\DateTimeImmutable $updatedAt;
     public ?\DateTimeImmutable $createdAt;
@@ -30,8 +32,6 @@ class UserData implements \JsonSerializable
      * User constructor.
      *
      * @param array $userData
-     *
-     * @throws \Exception
      */
     public function __construct(array $userData = [])
     {
@@ -43,6 +43,7 @@ public function __construct(array $userData = [])
         $this->password = $userData['password'] ?? null;
         $this->password2 = $userData['password2'] ?? null;
         $this->passwordHash = $userData['password_hash'] ?? null;
+        $this->theme = $userData['theme'] ?? null ? UserTheme::tryFrom($userData['theme']) : null;
         $this->updatedAt = $userData['updated_at'] ?? null ? new \DateTimeImmutable($userData['updated_at']) : null;
         $this->createdAt = $userData['created_at'] ?? null ? new \DateTimeImmutable($userData['created_at']) : null;
         $this->status = $userData['status'] ?? null ? UserStatus::tryFrom($userData['status']) : null;
diff --git a/src/Domain/User/Enum/UserStatus.php b/src/Domain/User/Enum/UserStatus.php
index 5e1e914e..2906baaa 100644
--- a/src/Domain/User/Enum/UserStatus.php
+++ b/src/Domain/User/Enum/UserStatus.php
@@ -11,7 +11,7 @@ enum UserStatus: string
 {
     use EnumToArray;
 
-    // First letter uppercase and rest lowercase as names are used as labels in html form
+    // First letter uppercase and rest lowercase because these names are used as labels in html form as they are
     case Unverified = 'unverified'; // Default after registration
     case Active = 'active'; // Verified via token received in email
     case Locked = 'locked'; // Locked for security reasons, may be reactivated by account holder via email
diff --git a/src/Domain/User/Enum/UserTheme.php b/src/Domain/User/Enum/UserTheme.php
new file mode 100644
index 00000000..e2e032a6
--- /dev/null
+++ b/src/Domain/User/Enum/UserTheme.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace App\Domain\User\Enum;
+
+enum UserTheme: string
+{
+    case light = 'light';
+    case dark = 'dark';
+}
diff --git a/src/Domain/User/Service/UserFinder.php b/src/Domain/User/Service/UserFinder.php
index a64dafc7..09b08663 100644
--- a/src/Domain/User/Service/UserFinder.php
+++ b/src/Domain/User/Service/UserFinder.php
@@ -56,14 +56,11 @@ public function findAllUsersResultDataForList(): array
     /**
      * @param string|int $id
      *
-     * @throws \Exception
-     *
      * @return UserData
      */
     public function findUserById(string|int $id): UserData
     {
         // Find user in database and return object
-        // $notRestricted true as values are safe as they come from the database. It's not a user input.
         return new UserData($this->userFinderRepository->findUserById((int)$id));
     }
 
diff --git a/src/Domain/User/Service/UserUpdater.php b/src/Domain/User/Service/UserUpdater.php
index ffc63303..6a9cda46 100644
--- a/src/Domain/User/Service/UserUpdater.php
+++ b/src/Domain/User/Service/UserUpdater.php
@@ -52,6 +52,7 @@ public function updateUser(int $userIdToChange, array $userValues): bool
                     'email',
                     'status',
                     'user_role_id',
+                    'theme',
                 ], true)) {
                     $validUpdateData[$column] = $value;
                 } else {
diff --git a/src/Domain/User/Service/UserValidator.php b/src/Domain/User/Service/UserValidator.php
index 83aeb4f3..183b98a8 100644
--- a/src/Domain/User/Service/UserValidator.php
+++ b/src/Domain/User/Service/UserValidator.php
@@ -4,6 +4,7 @@
 
 use App\Domain\User\Data\UserData;
 use App\Domain\User\Enum\UserStatus;
+use App\Domain\User\Enum\UserTheme;
 use App\Domain\Validation\ValidationException;
 use App\Domain\Validation\ValidationResult;
 use App\Domain\Validation\Validator;
@@ -53,6 +54,14 @@ public function validateUserUpdate(int $userId, array $userValues): ValidationRe
         if (array_key_exists('status', $userValues)) {
             $this->validateUserStatus($userValues['status'], $validationResult, true);
         }
+        if (array_key_exists('theme', $userValues)) {
+            $this->validator->validateBackedEnum(
+                $userValues['theme'],
+                UserTheme::class,
+                'theme',
+                $validationResult
+            );
+        }
         if (array_key_exists('user_role_id', $userValues)) {
             $this->validateUserRoleId($userValues['user_role_id'], $validationResult, true);
         }
diff --git a/src/Domain/Validation/Validator.php b/src/Domain/Validation/Validator.php
index 6b3647aa..eea212c6 100644
--- a/src/Domain/Validation/Validator.php
+++ b/src/Domain/Validation/Validator.php
@@ -254,7 +254,7 @@ public function validateNumeric(
      * @template Enum
      *
      * @param \BackedEnum|string|null $value enum case or backed string value
-     * @param class-string $enum
+     * @param class-string $enum e.g. UserRole::class
      * @param string $fieldName
      * @param ValidationResult $validationResult
      * @param bool $required
diff --git a/src/Infrastructure/User/UserFinderRepository.php b/src/Infrastructure/User/UserFinderRepository.php
index 4b779846..421b709f 100644
--- a/src/Infrastructure/User/UserFinderRepository.php
+++ b/src/Infrastructure/User/UserFinderRepository.php
@@ -19,6 +19,7 @@ class UserFinderRepository
         'status',
         'updated_at',
         'created_at',
+        'theme',
     ];
 
     public function __construct(
diff --git a/templates/layout.html.php b/templates/layout.html.php
index 264d2c75..95f5bb3e 100644
--- a/templates/layout.html.php
+++ b/templates/layout.html.php
@@ -52,9 +52,16 @@
 
     <title><?= $title ?></title>
     <script>
-        // If a theme is set in localstorage, add it immediately to the <html> element before everything is done loading
-        const theme = localStorage.getItem('theme') ? localStorage.getItem('theme') : 'light';
-        document.documentElement.setAttribute('data-theme', theme);
+        // Add the theme immediately to the <html> element before everything is done loading
+        const theme = localStorage.getItem('theme') ? localStorage.getItem('theme') : null;
+        // Get the theme provided from the server via query param (only after login)
+        const themeParam = new URLSearchParams(window.location.search).get('theme');
+        // Finally add the theme to the <html> element
+        document.documentElement.setAttribute('data-theme', themeParam ?? theme ?? 'light');
+        // If a theme from the database is provided and not the same with localStorage, replace it
+        if (themeParam && themeParam !== theme) {
+            localStorage.setItem('theme', themeParam);
+        }
     </script>
 </head>
 <body>
diff --git a/templates/user/user-read.html.php b/templates/user/user-read.html.php
index aee06b75..2629d162 100644
--- a/templates/user/user-read.html.php
+++ b/templates/user/user-read.html.php
@@ -81,7 +81,7 @@ class="contenteditable-edit-icon cursor-pointer"
                         echo "<option value='$userStatus->value' $selected>" .
                             ucfirst($userStatus->value) . "</option>";
                     }
-?>
+                    ?>
                 </select>
             </div>
 
@@ -91,11 +91,11 @@ class="contenteditable-edit-icon cursor-pointer"
                 <select name="user_role_id" class="default-select bigger-select" id="user-role-select"
                     <?= $user->userRolePrivilege->hasPrivilege(Privilege::UPDATE) ? '' : 'disabled' ?>>
                     <?php
-foreach ($user->availableUserRoles as $id => $userRole) {
-    $selected = $id === $user->userRoleId ? 'selected' : '';
-    echo "<option value='$id' $selected>" . $userRole . "</option>";
-}
-?>
+                    foreach ($user->availableUserRoles as $id => $userRole) {
+                        $selected = $id === $user->userRoleId ? 'selected' : '';
+                        echo "<option value='$id' $selected>" . $userRole . "</option>";
+                    }
+                    ?>
                 </select>
             </div>
         </div>
@@ -126,23 +126,26 @@ class="contenteditable-edit-icon cursor-pointer"
                 <?php
             } ?>
         </div>
-        <div>
-            <h3 class="label-h3">Dark mode</h3>
-            <label id="dark-mode-switch-container">
-                <input id='dark-mode-toggle-checkbox' type='checkbox'>
-                <div id='dark-mode-toggle-slot'>
-                    <div id='dark-mode-sun-icon-wrapper'>
-                        <!--<div class="iconify" id="dark-mode-sun-icon" data-icon="feather-sun" data-inline="false"></div>-->
-                        <img src="assets/general/dark-mode/sun-icon.svg" alt="sun" id="dark-mode-sun-icon">
-                    </div>
-                    <div id="dark-mode-toggle-button"></div>
-                    <div id='dark-mode-moon-icon-wrapper'>
-                        <img src="assets/general/dark-mode/moon-icon.svg" alt="sun" id="dark-mode-moon-icon">
+        <?php
+        if ($isOwnProfile === true) { ?>
+            <div>
+                <h3 class="label-h3">Dark mode</h3>
+                <label id="dark-mode-switch-container">
+                    <input id='dark-mode-toggle-checkbox' type='checkbox'>
+                    <div id='dark-mode-toggle-slot'>
+                        <div id='dark-mode-sun-icon-wrapper'>
+                            <!--<div class="iconify" id="dark-mode-sun-icon" data-icon="feather-sun" data-inline="false"></div>-->
+                            <img src="assets/general/dark-mode/sun-icon.svg" alt="sun" id="dark-mode-sun-icon">
+                        </div>
+                        <div id="dark-mode-toggle-button"></div>
+                        <div id='dark-mode-moon-icon-wrapper'>
+                            <img src="assets/general/dark-mode/moon-icon.svg" alt="sun" id="dark-mode-moon-icon">
+                        </div>
                     </div>
-                </div>
-            </label>
-        </div>
-
+                </label>
+            </div>
+            <?php
+        } ?>
         <h3 class="label-h3">Metadata</h3>
         <p class="secondary-text"><b>ID:</b> <?= $user->id ?><br>
             <b>Created:</b> <?= $user->createdAt->format('d. F Y • H:i:s') ?><br>
diff --git a/tests/Integration/User/UserUpdateActionTest.php b/tests/Integration/User/UserUpdateActionTest.php
index 37379344..87d45324 100644
--- a/tests/Integration/User/UserUpdateActionTest.php
+++ b/tests/Integration/User/UserUpdateActionTest.php
@@ -21,7 +21,7 @@
 use Slim\Exception\HttpBadRequestException;
 
 /**
- * Integration testing user update Process.
+ * Integration testing user update.
  */
 class UserUpdateActionTest extends TestCase
 {
diff --git a/tests/Provider/User/UserUpdateProvider.php b/tests/Provider/User/UserUpdateProvider.php
index b8f9b991..255114cb 100644
--- a/tests/Provider/User/UserUpdateProvider.php
+++ b/tests/Provider/User/UserUpdateProvider.php
@@ -13,7 +13,7 @@ class UserUpdateProvider
     /**
      * @return array[]
      */
-    public function userUpdateAuthorizationCases(): array
+    public static function userUpdateAuthorizationCases(): array
     {
         // Set different user role attributes
         $managingAdvisorAttr = ['user_role_id' => UserRole::MANAGING_ADVISOR];
@@ -41,6 +41,7 @@ public function userUpdateAuthorizationCases(): array
             'first_name' => 'NewFirstName',
             'surname' => 'NewLastName',
             'email' => 'new.email@test.ch',
+            'theme' => 'dark',
             // Password hash change tested in UserChangePasswordActionTest
         ];
         // To avoid testing each column separately for each user role, the most basic change is taken to test
@@ -111,7 +112,7 @@ public function userUpdateAuthorizationCases(): array
      *
      * @return array
      */
-    public function invalidUserUpdateCases(): array
+    public static function invalidUserUpdateCases(): array
     {
         // Including as many values as possible that trigger validation errors in each case
         return [
@@ -123,6 +124,7 @@ public function invalidUserUpdateCases(): array
                     'email' => 'new.email@tes$t.ch',
                     'status' => 'non-existing',
                     'user_role_id' => 99,
+                    'theme' => 'invalid',
                 ],
                 'json_response' => [
                     'status' => 'error',
@@ -134,6 +136,7 @@ public function invalidUserUpdateCases(): array
                             ['field' => 'surname', 'message' => 'Minimum length is 2'],
                             ['field' => 'email', 'message' => 'Invalid email address'],
                             ['field' => 'status', 'message' => 'Status not existing'],
+                            ['field' => 'theme', 'message' => 'theme not existing'],
                             ['field' => 'user_role', 'message' => 'User role not existing'],
                         ],
                     ],