diff --git a/django/contrib/admin/static/admin/css/forms.css b/django/contrib/admin/static/admin/css/forms.css
index ae697cf58d..c6ce78833e 100644
--- a/django/contrib/admin/static/admin/css/forms.css
+++ b/django/contrib/admin/static/admin/css/forms.css
@@ -169,6 +169,10 @@ form .aligned select + div.help {
     padding-left: 10px;
 }
 
+form .aligned select option:checked {
+    background-color: var(--selected-row);
+}
+
 form .aligned ul li {
     list-style: none;
 }
diff --git a/docs/releases/5.1.2.txt b/docs/releases/5.1.2.txt
index 2727b112dc..a7293654df 100644
--- a/docs/releases/5.1.2.txt
+++ b/docs/releases/5.1.2.txt
@@ -16,3 +16,7 @@ Bugfixes
 
 * Fixed a regression in Django 5.1 that caused a crash of ``JSONObject()``
   when using server-side binding with PostgreSQL 16+ (:ticket:`35734`).
+
+* Fixed a regression in Django 5.1 that made selected items in multi-select
+  widgets indistinguishable from non-selected items in the admin dark theme
+  (:ticket:`35809`).
diff --git a/tests/admin_views/tests.py b/tests/admin_views/tests.py
index 16d76f5da2..f63a9ca56f 100644
--- a/tests/admin_views/tests.py
+++ b/tests/admin_views/tests.py
@@ -6175,6 +6175,65 @@ class SeleniumTests(AdminSeleniumTestCase):
         )
         self.take_screenshot("selectbox-non-collapsible")
 
+    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
+    def test_selectbox_selected_rows(self):
+        from selenium.webdriver import ActionChains
+        from selenium.webdriver.common.by import By
+        from selenium.webdriver.common.keys import Keys
+
+        self.admin_login(
+            username="super", password="secret", login_url=reverse("admin:index")
+        )
+        # Create a new user to ensure that no extra permissions have been set.
+        user = User.objects.create_user(username="new", password="newuser")
+        url = self.live_server_url + reverse("admin:auth_user_change", args=[user.id])
+        self.selenium.get(url)
+
+        # Scroll to the User permissions section.
+        user_permissions = self.selenium.find_element(
+            By.CSS_SELECTOR, "#id_user_permissions_from"
+        )
+        ActionChains(self.selenium).move_to_element(user_permissions).perform()
+        self.take_screenshot("selectbox-available-perms-none-selected")
+
+        # Select multiple permissions from the "Available" list.
+        ct = ContentType.objects.get_for_model(Permission)
+        perms = list(Permission.objects.filter(content_type=ct))
+        for perm in perms:
+            elem = self.selenium.find_element(
+                By.CSS_SELECTOR, f"#id_user_permissions_from option[value='{perm.id}']"
+            )
+            ActionChains(self.selenium).key_down(Keys.CONTROL).click(elem).key_up(
+                Keys.CONTROL
+            ).perform()
+
+        # Move focus to other element.
+        self.selenium.find_element(
+            By.CSS_SELECTOR, "#id_user_permissions_input"
+        ).click()
+        self.take_screenshot("selectbox-available-perms-some-selected")
+
+        # Move permissions to the "Chosen" list, but none is selected yet.
+        self.selenium.find_element(
+            By.CSS_SELECTOR, "#id_user_permissions_add_link"
+        ).click()
+        self.take_screenshot("selectbox-chosen-perms-none-selected")
+
+        # Select some permissions from the "Chosen" list.
+        for perm in [perms[0], perms[-1]]:
+            elem = self.selenium.find_element(
+                By.CSS_SELECTOR, f"#id_user_permissions_to option[value='{perm.id}']"
+            )
+            ActionChains(self.selenium).key_down(Keys.CONTROL).click(elem).key_up(
+                Keys.CONTROL
+            ).perform()
+
+        # Move focus to other element.
+        self.selenium.find_element(
+            By.CSS_SELECTOR, "#id_user_permissions_selected_input"
+        ).click()
+        self.take_screenshot("selectbox-chosen-perms-some-selected")
+
     @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
     def test_first_field_focus(self):
         """JavaScript-assisted auto-focus on first usable form field."""