diff --git a/core/modules/block/tests/src/Kernel/NewDefaultThemeBlocksTest.php b/core/modules/block/tests/src/Kernel/NewDefaultThemeBlocksTest.php
index b45f968aa6..129ac55682 100644
--- a/core/modules/block/tests/src/Kernel/NewDefaultThemeBlocksTest.php
+++ b/core/modules/block/tests/src/Kernel/NewDefaultThemeBlocksTest.php
@@ -6,7 +6,7 @@
 use Drupal\Tests\block\Traits\BlockCreationTrait;
 
 /**
- * Tests that the new default theme gets blocks.
+ * Tests that a new default theme gets blocks.
  *
  * @group block
  */
@@ -23,7 +23,7 @@ class NewDefaultThemeBlocksTest extends KernelTestBase {
   ];
 
   /**
-   * Check the enabled Bartik blocks are correctly copied over.
+   * Check the blocks are correctly copied by block_themes_installed().
    */
   public function testNewDefaultThemeBlocks() {
     $this->installConfig(['system']);
@@ -44,8 +44,8 @@ public function testNewDefaultThemeBlocks() {
       'id' => $default_theme . '_' . strtolower($this->randomMachineName(8)),
     ]);
 
-    // Install a different theme.
-    $new_theme = 'bartik';
+    // Install a different theme that does not have blocks.
+    $new_theme = 'test_theme';
     // The new theme is different from the previous default theme.
     $this->assertNotEquals($new_theme, $default_theme);
 
@@ -69,7 +69,7 @@ public function testNewDefaultThemeBlocks() {
     foreach ($default_block_names as $default_block_name) {
       // Remove the matching block from the list of blocks in the new theme.
       // E.g., if the old theme has block.block.stark_admin,
-      // unset block.block.bartik_admin.
+      // unset block.block.olivero_admin.
       unset($new_blocks[str_replace($default_theme . '_', $new_theme . '_', $default_block_name)]);
     }
     $this->assertEmpty($new_blocks);
diff --git a/core/modules/config/tests/src/Functional/ConfigImportUITest.php b/core/modules/config/tests/src/Functional/ConfigImportUITest.php
index f91aba49b9..395166d00f 100644
--- a/core/modules/config/tests/src/Functional/ConfigImportUITest.php
+++ b/core/modules/config/tests/src/Functional/ConfigImportUITest.php
@@ -88,18 +88,16 @@ public function testImport() {
     $core_extension['module']['automated_cron'] = 0;
     $core_extension['module']['ban'] = 0;
     $core_extension['module'] = module_config_sort($core_extension['module']);
-    // Bartik is a subtheme of Stable so Stable must be enabled.
-    $core_extension['theme']['stable'] = 0;
-    $core_extension['theme']['bartik'] = 0;
+    $core_extension['theme']['olivero'] = 0;
     $sync->write('core.extension', $core_extension);
 
     // Use the install storage so that we can read configuration from modules
     // and themes that are not installed.
     $install_storage = new InstallStorage();
 
-    // Set the Bartik theme as default.
+    // Set the Olivero theme as default.
     $system_theme = $this->config('system.theme')->get();
-    $system_theme['default'] = 'bartik';
+    $system_theme['default'] = 'olivero';
     $sync->write('system.theme', $system_theme);
 
     // Read the automated_cron config from module default config folder.
@@ -155,7 +153,7 @@ public function testImport() {
     $this->assertTrue(\Drupal::moduleHandler()->moduleExists('automated_cron'), 'Automated Cron module installed during import.');
     $this->assertTrue(\Drupal::moduleHandler()->moduleExists('options'), 'Options module installed during import.');
     $this->assertTrue(\Drupal::moduleHandler()->moduleExists('text'), 'Text module installed during import.');
-    $this->assertTrue(\Drupal::service('theme_handler')->themeExists('bartik'), 'Bartik theme installed during import.');
+    $this->assertTrue(\Drupal::service('theme_handler')->themeExists('olivero'), 'Olivero theme installed during import.');
 
     // Ensure installations and uninstallation occur as expected.
     $installed = \Drupal::state()->get('ConfigImportUITest.core.extension.modules_installed', []);
@@ -177,7 +175,7 @@ public function testImport() {
     unset($core_extension['module']['ban']);
     unset($core_extension['module']['options']);
     unset($core_extension['module']['text']);
-    unset($core_extension['theme']['bartik']);
+    unset($core_extension['theme']['olivero']);
     $sync->write('core.extension', $core_extension);
     $sync->delete('automated_cron.settings');
     $sync->delete('text.settings');
@@ -221,7 +219,7 @@ public function testImport() {
     $this->assertEmpty($installed, 'No modules installed during import');
 
     $theme_info = \Drupal::service('theme_handler')->listInfo();
-    $this->assertFalse(isset($theme_info['bartik']), 'Bartik theme uninstalled during import.');
+    $this->assertFalse(isset($theme_info['olivero']), 'Olivero theme uninstalled during import.');
 
     // Verify that the automated_cron.settings configuration object was only
     // deleted once during the import process.
@@ -511,7 +509,6 @@ public function testExtensionValidation() {
     unset($core['module']['text']);
     $module_data = $this->container->get('extension.list.module')->getList();
     $this->assertTrue(isset($module_data['node']->requires['text']), 'The Node module depends on the Text module.');
-    // Bartik depends on Stable.
     unset($core['theme']['test_basetheme']);
     $theme_data = \Drupal::service('theme_handler')->rebuildThemeData();
     $this->assertTrue(isset($theme_data['test_subtheme']->requires['test_basetheme']), 'The Test Subtheme theme depends on the Test Basetheme theme.');
diff --git a/core/modules/image/tests/src/Kernel/ImageThemeFunctionTest.php b/core/modules/image/tests/src/Kernel/ImageThemeFunctionTest.php
index 1f9654e71a..0a4e4f37fe 100644
--- a/core/modules/image/tests/src/Kernel/ImageThemeFunctionTest.php
+++ b/core/modules/image/tests/src/Kernel/ImageThemeFunctionTest.php
@@ -187,7 +187,7 @@ public function testImageAltFunctionality() {
     // Test using alt directly with alt attribute.
     $image_with_alt_property = [
       '#theme' => 'image',
-      '#uri' => '/core/themes/bartik/logo.svg',
+      '#uri' => '/core/themes/olivero/logo.svg',
       '#alt' => 'Regular alt',
       '#title' => 'Test title',
       '#width' => '50%',
@@ -202,7 +202,7 @@ public function testImageAltFunctionality() {
     // Test using alt attribute inside attributes.
     $image_with_alt_attribute_alt_attribute = [
       '#theme' => 'image',
-      '#uri' => '/core/themes/bartik/logo.svg',
+      '#uri' => '/core/themes/olivero/logo.svg',
       '#width' => '50%',
       '#height' => '50%',
       '#attributes' => [
@@ -220,7 +220,7 @@ public function testImageAltFunctionality() {
     // Test using alt attribute as property and inside attributes.
     $image_with_alt_attribute_both = [
       '#theme' => 'image',
-      '#uri' => '/core/themes/bartik/logo.svg',
+      '#uri' => '/core/themes/olivero/logo.svg',
       '#width' => '50%',
       '#height' => '50%',
       '#alt' => 'Kitten sustainable',
diff --git a/core/modules/system/tests/modules/common_test/common_test.module b/core/modules/system/tests/modules/common_test/common_test.module
index 3f25250abb..b38d5f7bbe 100644
--- a/core/modules/system/tests/modules/common_test/common_test.module
+++ b/core/modules/system/tests/modules/common_test/common_test.module
@@ -52,7 +52,7 @@ function common_test_drupal_alter_alter(&$data, &$arg2 = NULL, &$arg3 = NULL) {
  * Same as common_test_drupal_alter_alter(), but here, we verify that themes
  * can also alter and come last.
  */
-function bartik_drupal_alter_alter(&$data, &$arg2 = NULL, &$arg3 = NULL) {
+function olivero_drupal_alter_alter(&$data, &$arg2 = NULL, &$arg3 = NULL) {
   // Alter first argument.
   if (is_array($data)) {
     $data['foo'] .= ' theme';
diff --git a/core/modules/system/tests/src/Functional/Batch/PageTest.php b/core/modules/system/tests/src/Functional/Batch/PageTest.php
index 1d1854dc09..5261d15aef 100644
--- a/core/modules/system/tests/src/Functional/Batch/PageTest.php
+++ b/core/modules/system/tests/src/Functional/Batch/PageTest.php
@@ -29,10 +29,10 @@ class PageTest extends BrowserTestBase {
   public function testBatchProgressPageTheme() {
     // Make sure that the page which starts the batch (an administrative page)
     // is using a different theme than would normally be used by the batch API.
-    $this->container->get('theme_installer')->install(['seven', 'bartik']);
+    $this->container->get('theme_installer')->install(['claro', 'olivero']);
     $this->config('system.theme')
-      ->set('default', 'bartik')
-      ->set('admin', 'seven')
+      ->set('default', 'olivero')
+      ->set('admin', 'claro')
       ->save();
 
     // Log in as an administrator who can see the administrative theme.
@@ -45,7 +45,7 @@ public function testBatchProgressPageTheme() {
     $this->drupalGet('admin/batch-test/test-theme');
     // The stack should contain the name of the theme used on the progress
     // page.
-    $this->assertEquals(['seven'], batch_test_stack(), 'A progressive batch correctly uses the theme of the page that started the batch.');
+    $this->assertEquals(['claro'], batch_test_stack(), 'A progressive batch correctly uses the theme of the page that started the batch.');
   }
 
   /**
diff --git a/core/modules/system/tests/src/Functional/Common/AlterTest.php b/core/modules/system/tests/src/Functional/Common/AlterTest.php
index 14122c8bc9..1c9e7de890 100644
--- a/core/modules/system/tests/src/Functional/Common/AlterTest.php
+++ b/core/modules/system/tests/src/Functional/Common/AlterTest.php
@@ -27,10 +27,10 @@ class AlterTest extends BrowserTestBase {
    * Tests if the theme has been altered.
    */
   public function testDrupalAlter() {
-    // This test depends on Bartik, so make sure that it is always the current
+    // This test depends on Olivero, so make sure that it is always the current
     // active theme.
-    \Drupal::service('theme_installer')->install(['bartik']);
-    \Drupal::theme()->setActiveTheme(\Drupal::service('theme.initialization')->initTheme('bartik'));
+    \Drupal::service('theme_installer')->install(['olivero']);
+    \Drupal::theme()->setActiveTheme(\Drupal::service('theme.initialization')->initTheme('olivero'));
 
     $array = ['foo' => 'bar'];
     $entity = new \stdClass();
diff --git a/core/modules/system/tests/src/Functional/Menu/MenuRouterTest.php b/core/modules/system/tests/src/Functional/Menu/MenuRouterTest.php
index 2208cf5b19..cbc591d873 100644
--- a/core/modules/system/tests/src/Functional/Menu/MenuRouterTest.php
+++ b/core/modules/system/tests/src/Functional/Menu/MenuRouterTest.php
@@ -241,8 +241,8 @@ public function testAuthUserUserLogin() {
    * Tests theme integration.
    */
   public function testThemeIntegration() {
-    $this->defaultTheme = 'bartik';
-    $this->adminTheme = 'seven';
+    $this->defaultTheme = 'olivero';
+    $this->adminTheme = 'claro';
 
     /** @var \Drupal\Core\Extension\ThemeInstallerInterface $theme_installer */
     $theme_installer = $this->container->get('theme_installer');
@@ -269,8 +269,8 @@ public function testThemeIntegration() {
    */
   protected function doTestThemeCallbackAdministrative() {
     $this->drupalGet('menu-test/theme-callback/use-admin-theme');
-    $this->assertSession()->pageTextContains('Active theme: seven. Actual theme: seven.');
-    $this->assertSession()->responseContains('seven/css/base/elements.css');
+    $this->assertSession()->pageTextContains('Active theme: claro. Actual theme: claro.');
+    $this->assertSession()->responseContains('claro/css/base/elements.css');
   }
 
   /**
@@ -283,15 +283,15 @@ protected function doTestThemeCallbackMaintenanceMode() {
     // we expect the theme callback system to be bypassed entirely.
     $this->drupalGet('menu-test/theme-callback/use-admin-theme');
     // Check that the maintenance theme's CSS appears on the page.
-    $this->assertSession()->responseContains('bartik/css/base/elements.css');
+    $this->assertSession()->responseContains('olivero/css/base/base.css');
 
     // An administrator, however, should continue to see the requested theme.
     $admin_user = $this->drupalCreateUser(['access site in maintenance mode']);
     $this->drupalLogin($admin_user);
     $this->drupalGet('menu-test/theme-callback/use-admin-theme');
-    $this->assertSession()->pageTextContains('Active theme: seven. Actual theme: seven.');
+    $this->assertSession()->pageTextContains('Active theme: claro. Actual theme: claro.');
     // Check that the administrative theme's CSS appears on the page.
-    $this->assertSession()->responseContains('seven/css/base/elements.css');
+    $this->assertSession()->responseContains('claro/css/base/elements.css');
 
     $this->container->get('state')->set('system.maintenance_mode', FALSE);
   }
@@ -302,9 +302,9 @@ protected function doTestThemeCallbackMaintenanceMode() {
   protected function doTestThemeCallbackOptionalTheme() {
     // Request a theme that is not installed.
     $this->drupalGet('menu-test/theme-callback/use-test-theme');
-    $this->assertSession()->pageTextContains('Active theme: bartik. Actual theme: bartik.');
+    $this->assertSession()->pageTextContains('Active theme: olivero. Actual theme: olivero.');
     // Check that the default theme's CSS appears on the page.
-    $this->assertSession()->responseContains('bartik/css/base/elements.css');
+    $this->assertSession()->responseContains('olivero/css/base/base.css');
 
     // Now install the theme and request it again.
     /** @var \Drupal\Core\Extension\ThemeInstallerInterface $theme_installer */
@@ -324,9 +324,9 @@ protected function doTestThemeCallbackOptionalTheme() {
    */
   protected function doTestThemeCallbackFakeTheme() {
     $this->drupalGet('menu-test/theme-callback/use-fake-theme');
-    $this->assertSession()->pageTextContains('Active theme: bartik. Actual theme: bartik.');
+    $this->assertSession()->pageTextContains('Active theme: olivero. Actual theme: olivero.');
     // Check that the default theme's CSS appears on the page.
-    $this->assertSession()->responseContains('bartik/css/base/elements.css');
+    $this->assertSession()->responseContains('olivero/css/base/base.css');
   }
 
   /**
@@ -334,9 +334,9 @@ protected function doTestThemeCallbackFakeTheme() {
    */
   protected function doTestThemeCallbackNoThemeRequested() {
     $this->drupalGet('menu-test/theme-callback/no-theme-requested');
-    $this->assertSession()->pageTextContains('Active theme: bartik. Actual theme: bartik.');
+    $this->assertSession()->pageTextContains('Active theme: olivero. Actual theme: olivero.');
     // Check that the default theme's CSS appears on the page.
-    $this->assertSession()->responseContains('bartik/css/base/elements.css');
+    $this->assertSession()->responseContains('olivero/css/base/base.css');
   }
 
 }
diff --git a/core/modules/system/tests/src/Functional/System/SiteMaintenanceTest.php b/core/modules/system/tests/src/Functional/System/SiteMaintenanceTest.php
index 61efe6f0f8..29fbd65d32 100644
--- a/core/modules/system/tests/src/Functional/System/SiteMaintenanceTest.php
+++ b/core/modules/system/tests/src/Functional/System/SiteMaintenanceTest.php
@@ -146,11 +146,11 @@ public function testSiteMaintenance() {
     $this->submitForm([], 'Log in');
     $this->assertSession()->pageTextContains($user_message);
 
-    // Regression test to check if title displays in Bartik on maintenance page.
-    \Drupal::service('theme_installer')->install(['bartik']);
-    $this->config('system.theme')->set('default', 'bartik')->save();
+    // Check if title displays in Olivero on maintenance page.
+    \Drupal::service('theme_installer')->install(['olivero']);
+    $this->config('system.theme')->set('default', 'olivero')->save();
 
-    // Logout and verify that offline message is displayed in Bartik.
+    // Logout and verify that offline message is displayed in Olivero.
     $this->drupalLogout();
     $this->drupalGet('');
     $this->assertEquals('Site under maintenance', $this->cssSelect('main h1')[0]->getText());
diff --git a/core/modules/system/tests/src/Functional/System/ThemeTest.php b/core/modules/system/tests/src/Functional/System/ThemeTest.php
index e74bf68b23..2275eaeb9f 100644
--- a/core/modules/system/tests/src/Functional/System/ThemeTest.php
+++ b/core/modules/system/tests/src/Functional/System/ThemeTest.php
@@ -60,7 +60,7 @@ protected function setUp(): void {
    */
   public function testThemeSettings() {
     // Ensure a disabled theme settings form URL returns 404.
-    $this->drupalGet('admin/appearance/settings/bartik');
+    $this->drupalGet('admin/appearance/settings/olivero');
     $this->assertSession()->statusCodeEquals(404);
     // Ensure a non existent theme settings form URL returns 404.
     $this->drupalGet('admin/appearance/settings/' . $this->randomMachineName());
@@ -194,14 +194,14 @@ public function testThemeSettings() {
     $this->drupalGet('');
     $this->assertSession()->elementAttributeContains('xpath', '//header//a[@rel="home"]/img', 'src', $file_url_generator->generateString($uploaded_filename));
 
-    $this->container->get('theme_installer')->install(['bartik']);
+    $this->container->get('theme_installer')->install(['olivero']);
 
     // Ensure only valid themes are listed in the local tasks.
     $this->drupalPlaceBlock('local_tasks_block', ['region' => 'header']);
     $this->drupalGet('admin/appearance/settings');
     $theme_handler = \Drupal::service('theme_handler');
     $this->assertSession()->linkExists($theme_handler->getName('classy'));
-    $this->assertSession()->linkExists($theme_handler->getName('bartik'));
+    $this->assertSession()->linkExists($theme_handler->getName('olivero'));
     $this->assertSession()->linkNotExists($theme_handler->getName('stable'));
 
     // If a hidden theme is an admin theme it should be viewable.
@@ -231,14 +231,14 @@ public function testThemeSettings() {
    * Tests the theme settings logo form.
    */
   public function testThemeSettingsLogo() {
-    // Visit Bartik's theme settings page to replace the logo.
-    $this->container->get('theme_installer')->install(['bartik']);
-    $this->drupalGet('admin/appearance/settings/bartik');
+    // Visit Olivero's theme settings page to replace the logo.
+    $this->container->get('theme_installer')->install(['olivero']);
+    $this->drupalGet('admin/appearance/settings/olivero');
     $edit = [
       'default_logo' => FALSE,
       'logo_path' => 'core/misc/druplicon.png',
     ];
-    $this->drupalGet('admin/appearance/settings/bartik');
+    $this->drupalGet('admin/appearance/settings/olivero');
     $this->submitForm($edit, 'Save configuration');
     $this->assertSession()->fieldValueEquals('default_logo', FALSE);
     $this->assertSession()->fieldValueEquals('logo_path', 'core/misc/druplicon.png');
@@ -255,7 +255,7 @@ public function testThemeSettingsLogo() {
    * Tests the 'rendered' cache tag is cleared when saving theme settings.
    */
   public function testThemeSettingsRenderCacheClear() {
-    $this->container->get('theme_installer')->install(['bartik']);
+    $this->container->get('theme_installer')->install(['olivero']);
     // Ensure the frontpage is cached for anonymous users. The render cache will
     // cleared by installing a theme.
     $this->drupalLogout();
@@ -265,9 +265,9 @@ public function testThemeSettingsRenderCacheClear() {
     $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'HIT');
 
     $this->drupalLogin($this->adminUser);
-    // Save Bartik's theme settings which should invalidate the 'rendered' cache
+    // Save Olivero's theme settings which should invalidate the 'rendered' cache
     // tag in \Drupal\system\EventSubscriber\ConfigCacheTag.
-    $this->drupalGet('admin/appearance/settings/bartik');
+    $this->drupalGet('admin/appearance/settings/olivero');
     $this->submitForm([], 'Save configuration');
     $this->drupalLogout();
     $this->drupalGet('');
@@ -369,15 +369,15 @@ public function testSwitchDefaultTheme() {
     $this->config('system.theme')->set('default', 'stark')->save();
     $this->drupalPlaceBlock('local_tasks_block');
 
-    // Install Bartik and set it as the default theme.
-    $theme_installer->install(['bartik']);
+    // Install Olivero and set it as the default theme.
+    $theme_installer->install(['olivero']);
     $this->drupalGet('admin/appearance');
     $this->clickLink('Set as default');
-    $this->assertEquals('bartik', $this->config('system.theme')->get('default'));
+    $this->assertEquals('olivero', $this->config('system.theme')->get('default'));
 
     // Test the default theme on the secondary links (blocks admin page).
     $this->drupalGet('admin/structure/block');
-    $this->assertSession()->pageTextContains('Bartik(active tab)');
+    $this->assertSession()->pageTextContains('Olivero(active tab)');
     // Switch back to Stark and test again to test that the menu cache is cleared.
     $this->drupalGet('admin/appearance');
     // Stark is the first 'Set as default' link.
@@ -413,8 +413,8 @@ public function testInvalidTheme() {
    * Tests uninstalling of themes works.
    */
   public function testUninstallingThemes() {
-    // Install Bartik and set it as the default theme.
-    \Drupal::service('theme_installer')->install(['bartik']);
+    // Install Olivero and set it as the default theme.
+    \Drupal::service('theme_installer')->install(['olivero']);
     // Set up seven as the admin theme.
     \Drupal::service('theme_installer')->install(['seven']);
     $edit = [
@@ -428,10 +428,10 @@ public function testUninstallingThemes() {
 
     // Check that seven cannot be uninstalled as it is the admin theme.
     $this->assertSession()->responseNotContains('Uninstall Seven theme');
-    // Check that bartik cannot be uninstalled as it is the default theme.
-    $this->assertSession()->responseNotContains('Uninstall Bartik theme');
+    // Check that olivero cannot be uninstalled as it is the default theme.
+    $this->assertSession()->responseNotContains('Uninstall Olivero theme');
     // Check that the classy theme cannot be uninstalled as it is a base theme
-    // of seven and bartik.
+    // of seven and olivero.
     $this->assertSession()->responseNotContains('Uninstall Classy theme');
 
     // Install Stark and set it as the default theme.
@@ -447,22 +447,22 @@ public function testUninstallingThemes() {
     // Check that seven can be uninstalled now.
     $this->assertSession()->responseContains('Uninstall Seven theme');
     // Check that the classy theme still cannot be uninstalled as it is a
-    // base theme of bartik.
+    // base theme of olivero.
     $this->assertSession()->responseNotContains('Uninstall Classy theme');
 
     // Change the default theme to stark, stark is second in the list.
     $this->clickLink('Set as default', 1);
 
-    // Check that bartik can be uninstalled now.
-    $this->assertSession()->responseContains('Uninstall Bartik theme');
+    // Check that olivero can be uninstalled now.
+    $this->assertSession()->responseContains('Uninstall Olivero theme');
 
     // Check that the classy theme still can't be uninstalled as neither of its
     // base themes have been.
     $this->assertSession()->responseNotContains('Uninstall Classy theme');
 
-    // Uninstall each of the three themes starting with Bartik.
+    // Uninstall each of the three themes starting with Olivero.
     $this->clickLink('Uninstall');
-    $this->assertSession()->responseContains('The <em class="placeholder">Bartik</em> theme has been uninstalled');
+    $this->assertSession()->responseContains('The <em class="placeholder">Olivero</em> theme has been uninstalled');
     // Seven is the second in the list.
     $this->clickLink('Uninstall');
     $this->assertSession()->responseContains('The <em class="placeholder">Seven</em> theme has been uninstalled');
@@ -476,7 +476,7 @@ public function testUninstallingThemes() {
    */
   public function testInstallAndSetAsDefault() {
     $themes = [
-      'bartik' => 'Bartik',
+      'olivero' => 'Olivero',
       'test_core_semver' => 'Theme test with semver core version',
     ];
     foreach ($themes as $theme_machine_name => $theme_name) {
diff --git a/core/modules/system/tests/src/Kernel/Entity/ConfigEntityImportTest.php b/core/modules/system/tests/src/Kernel/Entity/ConfigEntityImportTest.php
index a970c30257..0b3495dec8 100644
--- a/core/modules/system/tests/src/Kernel/Entity/ConfigEntityImportTest.php
+++ b/core/modules/system/tests/src/Kernel/Entity/ConfigEntityImportTest.php
@@ -39,7 +39,7 @@ class ConfigEntityImportTest extends KernelTestBase {
    */
   public function testConfigUpdateImport() {
     $this->installConfig(['action', 'block', 'filter', 'image']);
-    $this->container->get('theme_installer')->install(['bartik']);
+    $this->container->get('theme_installer')->install(['olivero']);
     $config_storage = $this->container->get('config.storage');
     // Ensure the 'system.site' config.
     $config_storage->write('system.site', ['uuid' => (new Php())->generate()]);
@@ -83,7 +83,7 @@ protected function doBlockUpdate() {
     $block = $this->placeBlock('system_powered_by_block', [
       'id' => 'apple',
       'label' => 'Red Delicious',
-      'theme' => 'bartik',
+      'theme' => 'olivero',
     ]);
 
     $this->checkSinglePluginConfigSync($block, 'settings', 'label', 'Red Delicious');
diff --git a/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php b/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
index ffd891cd14..347d438228 100644
--- a/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
+++ b/core/modules/system/tests/src/Kernel/Extension/ModuleHandlerTest.php
@@ -332,10 +332,10 @@ public function testModuleStreamWrappers() {
   public function testThemeMetaData() {
     // Generate the list of available themes.
     $themes = \Drupal::service('theme_handler')->rebuildThemeData();
-    // Check that the mtime field exists for the bartik theme.
-    $this->assertNotEmpty($themes['bartik']->info['mtime'], 'The bartik.info.yml file modification time field is present.');
+    // Check that the mtime field exists for the olivero theme.
+    $this->assertNotEmpty($themes['olivero']->info['mtime'], 'The olivero.info.yml file modification time field is present.');
     // Use 0 if mtime isn't present, to avoid an array index notice.
-    $test_mtime = !empty($themes['bartik']->info['mtime']) ? $themes['bartik']->info['mtime'] : 0;
+    $test_mtime = !empty($themes['olivero']->info['mtime']) ? $themes['olivero']->info['mtime'] : 0;
     // Ensure the mtime field contains a number that is greater than zero.
     $this->assertIsNumeric($test_mtime);
     $this->assertGreaterThan(0, $test_mtime);
diff --git a/core/modules/system/tests/src/Kernel/Theme/TwigNamespaceTest.php b/core/modules/system/tests/src/Kernel/Theme/TwigNamespaceTest.php
index f758ddd287..946dcc35da 100644
--- a/core/modules/system/tests/src/Kernel/Theme/TwigNamespaceTest.php
+++ b/core/modules/system/tests/src/Kernel/Theme/TwigNamespaceTest.php
@@ -31,7 +31,7 @@ class TwigNamespaceTest extends KernelTestBase {
 
   protected function setUp(): void {
     parent::setUp();
-    \Drupal::service('theme_installer')->install(['test_theme', 'bartik']);
+    \Drupal::service('theme_installer')->install(['test_theme', 'olivero']);
     $this->twig = \Drupal::service('twig');
   }
 
@@ -52,7 +52,7 @@ public function testTemplateDiscovery() {
     $this->assertTwigTemplate($this->twig->load('@node/node.html.twig'), 'Found node.html.twig in node module.');
 
     // Tests resolving namespaced templates in themes.
-    $this->assertTwigTemplate($this->twig->load('@bartik/page.html.twig'), 'Found page.html.twig in Bartik theme.');
+    $this->assertTwigTemplate($this->twig->load('@olivero/layout/page.html.twig'), 'Found page.html.twig in Olivero theme.');
   }
 
   /**
diff --git a/core/modules/system/tests/src/Unit/Menu/SystemLocalTasksTest.php b/core/modules/system/tests/src/Unit/Menu/SystemLocalTasksTest.php
index 9c59b4c48c..036c138cdc 100644
--- a/core/modules/system/tests/src/Unit/Menu/SystemLocalTasksTest.php
+++ b/core/modules/system/tests/src/Unit/Menu/SystemLocalTasksTest.php
@@ -31,17 +31,17 @@ protected function setUp(): void {
 
     $this->themeHandler = $this->createMock('Drupal\Core\Extension\ThemeHandlerInterface');
 
-    $theme = new Extension($this->root, 'theme', 'core/themes/bartik', 'bartik.info.yml');
+    $theme = new Extension($this->root, 'theme', 'core/themes/olivero', 'olivero.info.yml');
     $theme->status = 1;
-    $theme->info = ['name' => 'bartik'];
+    $theme->info = ['name' => 'olivero'];
     $this->themeHandler->expects($this->any())
       ->method('listInfo')
       ->will($this->returnValue([
-        'bartik' => $theme,
+        'olivero' => $theme,
       ]));
     $this->themeHandler->expects($this->any())
       ->method('hasUi')
-      ->with('bartik')
+      ->with('olivero')
       ->willReturn(TRUE);
     $this->container->set('theme_handler', $this->themeHandler);
   }
@@ -65,7 +65,7 @@ public function getSystemAdminRoutes() {
         'system.theme_settings_theme',
         [
           ['system.themes_page', 'system.theme_settings'],
-          ['system.theme_settings_global', 'system.theme_settings_theme:bartik'],
+          ['system.theme_settings_global', 'system.theme_settings_theme:olivero'],
         ],
       ],
     ];
diff --git a/core/modules/tour/tests/src/Functional/TourTest.php b/core/modules/tour/tests/src/Functional/TourTest.php
index c15d00f957..32e958dbbd 100644
--- a/core/modules/tour/tests/src/Functional/TourTest.php
+++ b/core/modules/tour/tests/src/Functional/TourTest.php
@@ -56,7 +56,7 @@ protected function setUp(): void {
     parent::setUp();
 
     $this->drupalPlaceBlock('local_actions_block', [
-      'theme' => 'seven',
+      'theme' => 'claro',
       'region' => 'content',
     ]);
   }
diff --git a/core/modules/tour/tests/src/Functional/TourTestBasic.php b/core/modules/tour/tests/src/Functional/TourTestBasic.php
index f0c9240bd5..6d4456d7d9 100644
--- a/core/modules/tour/tests/src/Functional/TourTestBasic.php
+++ b/core/modules/tour/tests/src/Functional/TourTestBasic.php
@@ -44,10 +44,10 @@ protected function setUp(): void {
 
     // Make sure we are using distinct default and administrative themes for
     // the duration of these tests.
-    $this->container->get('theme_installer')->install(['bartik', 'seven']);
+    $this->container->get('theme_installer')->install(['olivero', 'claro']);
     $this->config('system.theme')
-      ->set('default', 'bartik')
-      ->set('admin', 'seven')
+      ->set('default', 'olivero')
+      ->set('admin', 'claro')
       ->save();
 
     $this->permissions[] = 'view the administration theme';
diff --git a/core/modules/user/tests/src/Unit/Theme/AdminNegotiatorTest.php b/core/modules/user/tests/src/Unit/Theme/AdminNegotiatorTest.php
index ddbba3aa52..e4bcd038bb 100644
--- a/core/modules/user/tests/src/Unit/Theme/AdminNegotiatorTest.php
+++ b/core/modules/user/tests/src/Unit/Theme/AdminNegotiatorTest.php
@@ -35,7 +35,7 @@ public function testDetermineActiveTheme($admin_theme, $expected) {
    */
   public function getThemes() {
     return [
-      ['seven', 'seven'],
+      ['claro', 'claro'],
       [NULL, NULL],
       ['', NULL],
     ];
diff --git a/core/modules/views/tests/modules/views_test_config/test_views/views.view.test_area_order.yml b/core/modules/views/tests/modules/views_test_config/test_views/views.view.test_area_order.yml
index 31cdb9571a..6c898e74ba 100644
--- a/core/modules/views/tests/modules/views_test_config/test_views/views.view.test_area_order.yml
+++ b/core/modules/views/tests/modules/views_test_config/test_views/views.view.test_area_order.yml
@@ -19,14 +19,14 @@ display:
           field: entity_block
           id: entity_block
           table: views
-          target: 'bartik_powered'
+          target: 'id_olivero_powered'
           view_mode: full
           plugin_id: entity
         entity_block_1:
           field: entity_block
           id: entity_block
           table: views
-          target: 'bartik_branding'
+          target: 'id_olivero_branding'
           view_mode: full
           plugin_id: entity
       fields:
diff --git a/core/modules/views/tests/src/Kernel/Handler/AreaEntityTest.php b/core/modules/views/tests/src/Kernel/Handler/AreaEntityTest.php
index f81def4de0..786ebbb7a3 100644
--- a/core/modules/views/tests/src/Kernel/Handler/AreaEntityTest.php
+++ b/core/modules/views/tests/src/Kernel/Handler/AreaEntityTest.php
@@ -46,8 +46,8 @@ protected function setUp($import_test_views = TRUE): void {
    */
   protected function setUpFixtures() {
     // Install the themes used for this test.
-    $this->container->get('theme_installer')->install(['bartik']);
-    $this->container->get('config.factory')->getEditable('system.theme')->set('default', 'bartik')->save();
+    $this->container->get('theme_installer')->install(['olivero']);
+    $this->container->get('config.factory')->getEditable('system.theme')->set('default', 'olivero')->save();
 
     $this->installEntitySchema('user');
     $this->installEntitySchema('entity_test');
diff --git a/core/modules/views/tests/src/Kernel/Handler/AreaOrderTest.php b/core/modules/views/tests/src/Kernel/Handler/AreaOrderTest.php
index d95975dfbf..613f03444e 100644
--- a/core/modules/views/tests/src/Kernel/Handler/AreaOrderTest.php
+++ b/core/modules/views/tests/src/Kernel/Handler/AreaOrderTest.php
@@ -35,18 +35,18 @@ class AreaOrderTest extends ViewsKernelTestBase {
    */
   protected function setUpFixtures() {
     // Install the themes used for this test.
-    $this->container->get('theme_installer')->install(['bartik']);
+    $this->container->get('theme_installer')->install(['olivero']);
 
     $this->placeBlock('system_branding_block', [
-      'id' => 'bartik_branding',
-      'theme' => 'bartik',
+      'id' => 'id_olivero_branding',
+      'theme' => 'olivero',
       'plugin' => 'system_branding_block',
       'weight' => 1,
     ]);
 
     $this->placeBlock('system_powered_by_block', [
-      'id' => 'bartik_powered',
-      'theme' => 'bartik',
+      'id' => 'id_olivero_powered',
+      'theme' => 'olivero',
       'weight' => 2,
     ]);
 
@@ -61,11 +61,11 @@ public function testAreaOrder() {
     $renderable = $view->buildRenderable();
     $output = $this->render($renderable);
 
-    $position_powered = strpos($output, 'block-bartik-powered');
-    $position_branding = strpos($output, 'block-bartik-branding');
+    $position_powered = strpos($output, 'block-id-olivero-powered');
+    $position_branding = strpos($output, 'block-id-olivero-branding');
 
-    $this->assertNotEquals(0, $position_powered, 'ID bartik-powered found.');
-    $this->assertNotEquals(0, $position_branding, 'ID bartik-branding found');
+    $this->assertNotEquals(0, $position_powered, 'ID olivero-powered found.');
+    $this->assertNotEquals(0, $position_branding, 'ID olivero-branding found');
 
     // Make sure "powered" is before "branding", so it reflects the position
     // in the configuration, and not the weight of the blocks.