diff --git a/core/lib/Drupal/Core/Extension/ModuleInstaller.php b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
index 760dd5b6f8..a6cf5b7fb9 100644
--- a/core/lib/Drupal/Core/Extension/ModuleInstaller.php
+++ b/core/lib/Drupal/Core/Extension/ModuleInstaller.php
@@ -77,7 +77,7 @@ public function __construct($root, ModuleHandlerInterface $module_handler, Drupa
     $this->moduleHandler = $module_handler;
     $this->kernel = $kernel;
     if (is_null($extension_list_theme)) {
-      @trigger_error('The extension.list.theme service must be passed to ' . __NAMESPACE__ . '\ModuleInstaller::__construct. It was added in Drupal 8.9.0 and will be required before Drupal 10.0.0.', E_USER_DEPRECATED);
+      @trigger_error('The extension.list.theme service must be passed to ' . __NAMESPACE__ . '\ModuleInstaller::__construct(). It was added in drupal 8.9.0 and will be required before drupal 10.0.0.', E_USER_DEPRECATED);
       $extension_list_theme = \Drupal::service('extension.list.theme');
     }
     $this->themeExtensionList = $extension_list_theme;
diff --git a/core/lib/Drupal/Core/Extension/ModuleRequiredByThemesUninstallValidator.php b/core/lib/Drupal/Core/Extension/ModuleRequiredByThemesUninstallValidator.php
index 0598b031e1..86499f55ca 100644
--- a/core/lib/Drupal/Core/Extension/ModuleRequiredByThemesUninstallValidator.php
+++ b/core/lib/Drupal/Core/Extension/ModuleRequiredByThemesUninstallValidator.php
@@ -51,7 +51,7 @@ public function validate($module) {
     $themes_depending_on_module = $this->getThemesDependingOnModule($module);
     if (!empty($themes_depending_on_module)) {
       $module_name = $this->moduleExtensionList->get($module)->info['name'];
-      $theme_names = implode(", ", $themes_depending_on_module);
+      $theme_names = implode(', ', $themes_depending_on_module);
       $reasons[] = $this->formatPlural(count($themes_depending_on_module),
         'Required by the theme: @theme_names',
         'Required by the themes: @theme_names',
diff --git a/core/lib/Drupal/Core/Extension/ThemeInstaller.php b/core/lib/Drupal/Core/Extension/ThemeInstaller.php
index 0fa79fa7a3..9d61a4df97 100644
--- a/core/lib/Drupal/Core/Extension/ThemeInstaller.php
+++ b/core/lib/Drupal/Core/Extension/ThemeInstaller.php
@@ -113,7 +113,7 @@ public function __construct(ThemeHandlerInterface $theme_handler, ConfigFactoryI
     $this->logger = $logger;
     $this->state = $state;
     if ($module_extension_list === NULL) {
-      @trigger_error('The extension.list.module service must be passed to ' . __NAMESPACE__ . '\ThemeInstaller::__construct. It was added in Drupal 8.9.0 and will be required before Drupal 10.0.0.', E_USER_DEPRECATED);
+      @trigger_error('The extension.list.module service must be passed to ' . __NAMESPACE__ . '\ThemeInstaller::__construct(). It was added in drupal 8.9.0 and will be required before drupal 10.0.0.', E_USER_DEPRECATED);
       $module_extension_list = \Drupal::service('extension.list.module');
     }
     $this->moduleExtensionList = $module_extension_list;
@@ -126,8 +126,8 @@ public function install(array $theme_list, $install_dependencies = TRUE) {
     $extension_config = $this->configFactory->getEditable('core.extension');
 
     $theme_data = $this->themeHandler->rebuildThemeData();
-    $installed_themes = $this->configFactory->get('core.extension')->get('theme') ?: [];
-    $installed_modules = $this->configFactory->get('core.extension')->get('module') ?: [];
+    $installed_themes = $extension_config->get('theme') ?: [];
+    $installed_modules = $extension_config->get('module') ?: [];
 
     if ($install_dependencies) {
       $theme_list = array_combine($theme_list, $theme_list);
@@ -143,8 +143,8 @@ public function install(array $theme_list, $install_dependencies = TRUE) {
         return TRUE;
       }
 
+      $module_list = $this->moduleExtensionList->getList();
       foreach ($theme_list as $theme => $value) {
-        $module_list = $this->moduleExtensionList->getList();
         $module_dependencies = $theme_data[$theme]->module_dependencies;
         $theme_dependencies = array_diff_key($theme_data[$theme]->requires, $module_dependencies);
         $unmet_module_dependencies = array_diff_key($module_dependencies, $installed_modules);
diff --git a/core/modules/system/src/Controller/SystemController.php b/core/modules/system/src/Controller/SystemController.php
index 7e04f4c61d..5942ff3ce0 100644
--- a/core/modules/system/src/Controller/SystemController.php
+++ b/core/modules/system/src/Controller/SystemController.php
@@ -266,9 +266,8 @@ public function themesPage() {
             continue;
           }
 
-          // @todo add logic for not displaying hidden modules in
-          //   https://drupal.org/node/3117829
-
+          // @todo Add logic for not displaying hidden modules in
+          //   https://drupal.org/node/3117829.
           $module_name = $modules[$dependency]->info['name'];
           $theme->module_dependencies_list[$dependency] = $modules[$dependency]->status ? $this->t('@module_name', ['@module_name' => $module_name]) : $this->t('@module_name (<span class="admin-disabled">disabled</span>)', ['@module_name' => $module_name]);
 
diff --git a/core/modules/system/src/Form/ModulesListForm.php b/core/modules/system/src/Form/ModulesListForm.php
index c23bbc8915..d0c0a6fbb2 100644
--- a/core/modules/system/src/Form/ModulesListForm.php
+++ b/core/modules/system/src/Form/ModulesListForm.php
@@ -329,9 +329,8 @@ protected function buildRow(array $modules, Extension $module, $distribution) {
     // If this module requires other modules, add them to the array.
     /** @var \Drupal\Core\Extension\Dependency $dependency_object */
     foreach ($module->requires as $dependency => $dependency_object) {
-      // @todo add logic for not displaying hidden modules in
-      //   https://drupal.org/node/3117829
-
+      // @todo Add logic for not displaying hidden modules in
+      //   https://drupal.org/node/3117829.
       if ($incompatible = $this->checkDependencyMessage($modules, $dependency, $dependency_object)) {
         $row['#requires'][$dependency] = $incompatible;
         $row['enable']['#disabled'] = TRUE;
diff --git a/core/modules/system/tests/src/Functional/Form/ModulesListFormWebTest.php b/core/modules/system/tests/src/Functional/Form/ModulesListFormWebTest.php
index 5d5c7b3c91..f17ca8db1f 100644
--- a/core/modules/system/tests/src/Functional/Form/ModulesListFormWebTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ModulesListFormWebTest.php
@@ -87,12 +87,7 @@ public function testRequiredByThemeMessage() {
    * Creates user that can administer modules then visits `admin/modules`.
    */
   protected function createUserAdministerModules() {
-    $this->drupalLogin(
-      $this->drupalCreateUser(
-        ['administer modules', 'administer permissions']
-      )
-    );
-
+    $this->drupalLogin($this->drupalCreateUser(['administer modules', 'administer permissions']));
     $this->drupalGet('admin/modules');
     $this->assertSession()->statusCodeEquals(200);
   }
diff --git a/core/modules/system/tests/src/Functional/Theme/ThemeUiTest.php b/core/modules/system/tests/src/Functional/Theme/ThemeUiTest.php
index 1578f6dad6..b27fc124b3 100644
--- a/core/modules/system/tests/src/Functional/Theme/ThemeUiTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/ThemeUiTest.php
@@ -16,6 +16,11 @@ class ThemeUiTest extends BrowserTestBase {
    */
   protected $defaultTheme = 'stark';
 
+  /**
+   * Modules used for testing.
+   *
+   * @var array
+   */
   protected $testModules = [
     'help' => 'Help',
     'test_module_required_by_theme' => 'Test Module Required by Theme',
@@ -286,9 +291,8 @@ protected function assertUninstallableTheme(array $expected_requires_list_items,
       $this->assertTrue(in_array($item->getText(), $expected_requires_list_items));
     }
 
-    $incompatible = $theme_container->find('css', '.incompatible');
     $expected_incompatible_text = 'This theme requires the listed modules to operate correctly. They must first be enabled via the Extend page.';
-    $this->assertSame($expected_incompatible_text, $incompatible->getText());
+    $this->assertSession()->elementContains('css', '.incompatible', $expected_incompatible_text);
     $this->assertFalse($theme_container->hasLink('Install Test Theme Depending on Modules theme'));
   }