diff --git a/testing/web-platform/tests/css/css-shadow-parts/pseudo-classes-after-part.html b/testing/web-platform/tests/css/css-shadow-parts/pseudo-classes-after-part.html
index 60292d27a71c2..873df77139876 100644
--- a/testing/web-platform/tests/css/css-shadow-parts/pseudo-classes-after-part.html
+++ b/testing/web-platform/tests/css/css-shadow-parts/pseudo-classes-after-part.html
@@ -15,7 +15,6 @@
 test_valid_selector("::part(mypart):any-link");
 test_valid_selector("::part(mypart):autofill");
 test_valid_selector("::part(mypart):checked");
-test_valid_selector("::part(mypart):closed");
 test_valid_selector("::part(mypart):default");
 test_valid_selector("::part(mypart):defined");
 test_valid_selector("::part(mypart):dir(ltr)");
diff --git a/testing/web-platform/tests/css/selectors/open-closed-pseudo.html b/testing/web-platform/tests/css/selectors/open-pseudo.html
similarity index 63%
rename from testing/web-platform/tests/css/selectors/open-closed-pseudo.html
rename to testing/web-platform/tests/css/selectors/open-pseudo.html
index 9301fd2f41624..0f3b9f3c37966 100644
--- a/testing/web-platform/tests/css/selectors/open-closed-pseudo.html
+++ b/testing/web-platform/tests/css/selectors/open-pseudo.html
@@ -17,53 +17,39 @@
 <script>
 test(() => {
   const dialog = document.querySelector('dialog');
-  assert_true(dialog.matches(':closed'),
-    ':closed should match when the dialog is closed.');
   assert_false(dialog.matches(':open'),
     ':open should not match when the dialog is closed.');
 
   dialog.show();
-  assert_false(dialog.matches(':closed'),
-    ':closed should not match after dialog.open().');
   assert_true(dialog.matches(':open'),
     ':open should match after dialog.open().');
 
   dialog.close();
   dialog.showModal();
-  assert_false(dialog.matches(':closed'),
-    ':closed should not match after dialog.showModal().');
   assert_true(dialog.matches(':open'),
     ':open should match after dialog.showModal().');
 
   dialog.close();
-}, 'The dialog element should support :open and :closed.');
+}, 'The dialog element should support :open.');
 
 test(() => {
   const details = document.querySelector('details');
-  assert_true(details.matches(':closed'),
-    ':closed should match when the details is closed.');
   assert_false(details.matches(':open'),
     ':open should not match when the details is closed.');
 
   details.open = true;
-  assert_false(details.matches(':closed'),
-    ':closed should not match when the details is open.');
   assert_true(details.matches(':open'),
     ':open should match when the details is open.');
-}, 'The details element should support :open and :closed.');
+}, 'The details element should support :open.');
 
 promise_test(async () => {
   const select = document.querySelector('select');
-  assert_true(select.matches(':closed'),
-    ':closed should match when the select is closed.');
   assert_false(select.matches(':open'),
     ':open should not match when the select is closed.');
 
   await test_driver.click(select);
   await new Promise(requestAnimationFrame);
-  assert_false(select.matches(':closed'),
-    ':closed should not match when the select is open.');
   assert_true(select.matches(':open'),
     ':open should match when the select is open.');
-}, 'The select element should support :open and :closed.');
+}, 'The select element should support :open.');
 </script>
diff --git a/testing/web-platform/tests/html/semantics/forms/the-select-element/select-pseudo-light-dismiss-invalidation.tentative.html b/testing/web-platform/tests/html/semantics/forms/the-select-element/select-pseudo-light-dismiss-invalidation.tentative.html
index c9631d92e1258..749fd8cf27580 100644
--- a/testing/web-platform/tests/html/semantics/forms/the-select-element/select-pseudo-light-dismiss-invalidation.tentative.html
+++ b/testing/web-platform/tests/html/semantics/forms/the-select-element/select-pseudo-light-dismiss-invalidation.tentative.html
@@ -14,7 +14,7 @@
 select {
   background-color: rgb(0, 0, 255);
 }
-select:closed {
+select:not(:open) {
   background-color: rgb(0, 255, 0);
 }
 select:open {
@@ -29,7 +29,7 @@
 <script>
 promise_test(async () => {
   assert_equals(getComputedStyle(select).backgroundColor, 'rgb(0, 255, 0)',
-    'The select should match :closed at the start of the test.');
+    'The select should match :not(:open) at the start of the test.');
 
   await test_driver.click(select);
   assert_equals(getComputedStyle(select).backgroundColor, 'rgb(255, 0, 0)',
@@ -37,7 +37,7 @@
 
   await test_driver.click(opttwo);
   assert_equals(getComputedStyle(select).backgroundColor, 'rgb(0, 255, 0)',
-    'The select should match :closed after clicking an option.');
+    'The select should match :not(:open) after clicking an option.');
 
   await test_driver.click(select);
   assert_equals(getComputedStyle(select).backgroundColor, 'rgb(255, 0, 0)',
@@ -45,6 +45,6 @@
 
   await test_driver.click(button);
   assert_equals(getComputedStyle(select).backgroundColor, 'rgb(0, 255, 0)',
-    'The select should match :closed after light dismiss.');
+    'The select should match :not(:open) after light dismiss.');
 }, 'select should not match :open when light dismissed.');
 </script>