diff --git a/tests/src/Functional/EmailedExportFileDownloadAccessTest.php b/tests/src/Functional/EmailedExportFileDownloadAccessTest.php
index 575ec33..b2b5f29 100644
--- a/tests/src/Functional/EmailedExportFileDownloadAccessTest.php
+++ b/tests/src/Functional/EmailedExportFileDownloadAccessTest.php
@@ -14,6 +14,11 @@ use Drupal\webform_scheduled_tasks\Plugin\WebformScheduledTasks\Task\EmailedExpo
  */
 class EmailedExportFileDownloadAccessTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
diff --git a/tests/src/Functional/ScheduledTaskAdminFormTest.php b/tests/src/Functional/ScheduledTaskAdminFormTest.php
index ebbb3e1..5c80aad 100644
--- a/tests/src/Functional/ScheduledTaskAdminFormTest.php
+++ b/tests/src/Functional/ScheduledTaskAdminFormTest.php
@@ -12,6 +12,11 @@ use Drupal\webform_scheduled_tasks\Entity\WebformScheduledTask;
  */
 class ScheduledTaskAdminFormTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
diff --git a/tests/src/Functional/ScheduledTaskListBuilderTest.php b/tests/src/Functional/ScheduledTaskListBuilderTest.php
index a2a032b..dc5f8e9 100644
--- a/tests/src/Functional/ScheduledTaskListBuilderTest.php
+++ b/tests/src/Functional/ScheduledTaskListBuilderTest.php
@@ -13,6 +13,11 @@ use Drupal\webform_scheduled_tasks\Entity\WebformScheduledTask;
  */
 class ScheduledTaskListBuilderTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
diff --git a/tests/src/Functional/ScheduledTaskRunTest.php b/tests/src/Functional/ScheduledTaskRunTest.php
index 93a5e57..df83701 100644
--- a/tests/src/Functional/ScheduledTaskRunTest.php
+++ b/tests/src/Functional/ScheduledTaskRunTest.php
@@ -14,6 +14,11 @@ class ScheduledTaskRunTest extends BrowserTestBase {
 
   use CronRunTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
diff --git a/tests/src/FunctionalJavascript/EmailedExportUiTest.php b/tests/src/FunctionalJavascript/EmailedExportUiTest.php
index 3664f5a..4b2acc8 100644
--- a/tests/src/FunctionalJavascript/EmailedExportUiTest.php
+++ b/tests/src/FunctionalJavascript/EmailedExportUiTest.php
@@ -12,6 +12,11 @@ use Drupal\webform_scheduled_tasks\Entity\WebformScheduledTask;
  */
 class EmailedExportUiTest extends WebDriverTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *