diff --git a/core/modules/field/tests/src/Functional/Boolean/BooleanFieldTest.php b/core/modules/field/tests/src/Functional/Boolean/BooleanFieldTest.php
index 136ce8b923e..5e7ba126efc 100644
--- a/core/modules/field/tests/src/Functional/Boolean/BooleanFieldTest.php
+++ b/core/modules/field/tests/src/Functional/Boolean/BooleanFieldTest.php
@@ -29,7 +29,7 @@ class BooleanFieldTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  protected $defaultTheme = 'classy';
+  protected $defaultTheme = 'stark';
 
   /**
    * A field to use in this test class.
@@ -122,7 +122,7 @@ class BooleanFieldTest extends BrowserTestBase {
     // Verify that boolean value is displayed.
     $entity = EntityTest::load($id);
     $this->drupalGet($entity->toUrl());
-    $this->assertSession()->responseContains('<div class="field__item">' . $on . '</div>');
+    $this->assertSession()->pageTextContains($on);
 
     // Test with "On" label option.
     $display_repository->getFormDisplay('entity_test', 'entity_test')
diff --git a/core/modules/field/tests/src/Kernel/DisplayApiTest.php b/core/modules/field/tests/src/Kernel/DisplayApiTest.php
index b1fc135308e..a460678bb69 100644
--- a/core/modules/field/tests/src/Kernel/DisplayApiTest.php
+++ b/core/modules/field/tests/src/Kernel/DisplayApiTest.php
@@ -126,8 +126,8 @@ class DisplayApiTest extends FieldKernelTestBase {
   public function testFieldItemListView() {
     $items = $this->entity->get($this->fieldName);
 
-    \Drupal::service('theme_installer')->install(['classy']);
-    $this->config('system.theme')->set('default', 'classy')->save();
+    \Drupal::service('theme_installer')->install(['stark']);
+    $this->config('system.theme')->set('default', 'stark')->save();
 
     // No display settings: check that default display settings are used.
     $build = $items->view();
diff --git a/core/modules/field/tests/src/Kernel/EntityReference/EntityReferenceFormatterTest.php b/core/modules/field/tests/src/Kernel/EntityReference/EntityReferenceFormatterTest.php
index 6c335a91762..c025b2caf89 100644
--- a/core/modules/field/tests/src/Kernel/EntityReference/EntityReferenceFormatterTest.php
+++ b/core/modules/field/tests/src/Kernel/EntityReference/EntityReferenceFormatterTest.php
@@ -64,9 +64,9 @@ class EntityReferenceFormatterTest extends EntityKernelTestBase {
   protected function setUp(): void {
     parent::setUp();
 
-    // Use Classy theme for testing markup output.
-    \Drupal::service('theme_installer')->install(['classy']);
-    $this->config('system.theme')->set('default', 'classy')->save();
+    // Use Stark theme for testing markup output.
+    \Drupal::service('theme_installer')->install(['stark']);
+    $this->config('system.theme')->set('default', 'stark')->save();
     $this->installEntitySchema('entity_test');
     // Grant the 'view test entity' permission.
     $this->installConfig(['user']);
@@ -201,12 +201,12 @@ class EntityReferenceFormatterTest extends EntityKernelTestBase {
 
     // Test the first field item.
     $expected_rendered_name_field_1 = '
-            <div class="field field--name-name field--type-string field--label-hidden field__item">' . $this->referencedEntity->label() . '</div>
+            <div>' . $this->referencedEntity->label() . '</div>
       ';
     $expected_rendered_body_field_1 = '
-  <div class="clearfix text-formatted field field--name-body field--type-text field--label-above">
-    <div class="field__label">Body</div>
-              <div class="field__item"><p>Hello, world!</p></div>
+  <div>
+    <div>Body</div>
+              <div><p>Hello, world!</p></div>
           </div>
 ';
     $renderer->renderRoot($build[0]);
@@ -217,12 +217,12 @@ class EntityReferenceFormatterTest extends EntityKernelTestBase {
 
     // Test the second field item.
     $expected_rendered_name_field_2 = '
-            <div class="field field--name-name field--type-string field--label-hidden field__item">' . $this->unsavedReferencedEntity->label() . '</div>
+            <div>' . $this->unsavedReferencedEntity->label() . '</div>
       ';
     $expected_rendered_body_field_2 = '
-  <div class="clearfix text-formatted field field--name-body field--type-text field--label-above">
-    <div class="field__label">Body</div>
-              <div class="field__item"><p>Hello, unsaved world!</p></div>
+  <div>
+    <div>Body</div>
+              <div><p>Hello, unsaved world!</p></div>
           </div>
 ';
 
diff --git a/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php b/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php
index 61c65769b84..16493a5336e 100644
--- a/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php
+++ b/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php
@@ -20,7 +20,7 @@ class EntityDisplayTest extends WebDriverTestBase {
   /**
    * {@inheritdoc}
    */
-  protected $defaultTheme = 'classy';
+  protected $defaultTheme = 'stark';
 
   /**
    * {@inheritdoc}
@@ -74,7 +74,7 @@ class EntityDisplayTest extends WebDriverTestBase {
    */
   public function testEntityView() {
     $this->drupalGet('entity_test/1');
-    $this->assertSession()->elementNotExists('css', '.field--name-field-test-text');
+    $this->assertSession()->pageTextNotContains('The field test text value');
 
     $this->drupalGet('entity_test/structure/entity_test/display');
     $this->assertSession()->elementExists('css', '.region-content-message.region-empty');
@@ -91,7 +91,7 @@ class EntityDisplayTest extends WebDriverTestBase {
     $this->assertTrue($this->assertSession()->optionExists('fields[field_test_text][region]', 'content')->isSelected());
 
     $this->drupalGet('entity_test/1');
-    $this->assertSession()->elementExists('css', '.field--name-field-test-text');
+    $this->assertSession()->pageTextContains('The field test text value');
   }
 
   /**