diff --git a/core/modules/outside_in/css/off-canvas.base.css b/core/modules/outside_in/css/off-canvas.base.css
index 57cc85a097..a8bea702ef 100644
--- a/core/modules/outside_in/css/off-canvas.base.css
+++ b/core/modules/outside_in/css/off-canvas.base.css
@@ -13,6 +13,24 @@
 }
 
 /* Generic elements. */
+#drupal-off-canvas a,
+#drupal-off-canvas .link {
+  border-bottom: none;
+  font-family: "Lucida Grande", 'Lucida Sans Unicode','liberation sans', sans-serif;
+  font-size: inherit;
+  font-weight: normal;
+  color: #85bef4;
+  text-decoration: none;
+  transition: color .5s ease;
+}
+
+#drupal-off-canvas a:focus,
+#drupal-off-canvas .link:focus,
+#drupal-off-canvas a:hover,
+#drupal-off-canvas .link:hover {
+  outline: none;
+  color: #46a0f5;
+}
 #drupal-off-canvas hr {
   height: 1px;
   background: #cccccc;
diff --git a/core/modules/outside_in/css/off-canvas.theme.css b/core/modules/outside_in/css/off-canvas.theme.css
index e52ab37577..0de024f2c8 100644
--- a/core/modules/outside_in/css/off-canvas.theme.css
+++ b/core/modules/outside_in/css/off-canvas.theme.css
@@ -75,48 +75,6 @@
   right: 1em;
 }
 
-/* Style content in the tray.
-#drupal-off-canvas p,
-#drupal-off-canvas h1,
-#drupal-off-canvas h2,
-#drupal-off-canvas h3,
-#drupal-off-canvas h4,
-#drupal-off-canvas h5,
-#drupal-off-canvas h6,
-#drupal-off-canvas pre,
-#drupal-off-canvas legend,
-#drupal-off-canvas cite,
-#drupal-off-canvas span,
-#drupal-off-canvas summary,
-#drupal-off-canvas details,
-#drupal-off-canvas .form-item {
-  color: #ddd;
-  font-family: "Lucida Grande", 'Lucida Sans Unicode','liberation sans', sans-serif;
-  font-size: 14px;
-  font-weight: normal;
-  background-color: transparent;
-  text-shadow: none;
-}*/
-
-#drupal-off-canvas a,
-#drupal-off-canvas .link {
-  border-bottom: none;
-  font-family: "Lucida Grande", 'Lucida Sans Unicode','liberation sans', sans-serif;
-  font-size: inherit;
-  font-weight: normal;
-  color: #85bef4;
-  text-decoration: none;
-  transition: color .5s ease;
-}
-
-#drupal-off-canvas a:focus,
-#drupal-off-canvas .link:focus,
-#drupal-off-canvas a:hover,
-#drupal-off-canvas .link:hover {
-  outline: none;
-  color: #46a0f5;
-}
-
 /* Override default styling from jquery UI. */
 #drupal-off-canvas .ui-state-default,
 #drupal-off-canvas .ui-widget-content .ui-state-default,
diff --git a/core/modules/system/src/Form/RegionalForm.php b/core/modules/system/src/Form/RegionalForm.php
index a66b26b104..c365fc0551 100644
--- a/core/modules/system/src/Form/RegionalForm.php
+++ b/core/modules/system/src/Form/RegionalForm.php
@@ -65,7 +65,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
     $system_date = $this->config('system.date');
 
     // Date settings:
-    $zones = system_time_zones(NULL, TRUE);
+    $zones = system_time_zones();
 
     $form['locale'] = [
       '#type' => 'details',
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index d327d4e74b..a1a6b715a3 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -845,7 +845,7 @@ function system_user_timezone(&$form, FormStateInterface $form_state) {
     '#type' => 'select',
     '#title' => t('Time zone'),
     '#default_value' => $account->getTimezone() ? $account->getTimezone() : \Drupal::config('system.date')->get('timezone.default'),
-    '#options' => system_time_zones($account->id() != $user->id(), TRUE),
+    '#options' => system_time_zones($account->id() != $user->id()),
     '#description' => t('Select the desired local time and time zone. Dates and times throughout this site will be displayed using this time zone.'),
   ];
   $user_input = $form_state->getUserInput();
@@ -1355,15 +1355,10 @@ function system_mail($key, &$message, $params) {
 /**
  * Generate an array of time zones and their local time&date.
  *
- * @param mixed $blank
+ * @param $blank
  *   If evaluates true, prepend an empty time zone option to the array.
- * @param bool $grouped
- *   (optional) Whether the timezones should be grouped by region.
- *
- * @return array
- *   An array or nested array containing time zones, keyed by the system name.
  */
-function system_time_zones($blank = NULL, $grouped = FALSE) {
+function system_time_zones($blank = NULL) {
   $zonelist = timezone_identifiers_list();
   $zones = $blank ? ['' => t('- None selected -')] : [];
   foreach ($zonelist as $zone) {
@@ -1376,27 +1371,6 @@ function system_time_zones($blank = NULL, $grouped = FALSE) {
   }
   // Sort the translated time zones alphabetically.
   asort($zones);
-  if ($grouped) {
-    $grouped_zones = [];
-    foreach ($zones as $key => $value) {
-      $split = explode('/', $value);
-      $city = array_pop($split);
-      $region = array_shift($split);
-      if (!empty($region)) {
-        $grouped_zones[$region][$key] = empty($split) ? $city : $city . ' (' . join('/', $split) . ')';
-      }
-      else {
-        $grouped_zones[$key] = $value;
-      }
-    }
-    foreach ($grouped_zones as $key => $value) {
-      if (is_array($grouped_zones[$key])) {
-        asort($grouped_zones[$key]);
-      }
-    }
-    $zones = $grouped_zones;
-  }
-
   return $zones;
 }
 
diff --git a/core/modules/views/src/Plugin/views/field/Date.php b/core/modules/views/src/Plugin/views/field/Date.php
index 3014c2f6e0..37455cc783 100644
--- a/core/modules/views/src/Plugin/views/field/Date.php
+++ b/core/modules/views/src/Plugin/views/field/Date.php
@@ -119,7 +119,7 @@ public function buildOptionsForm(&$form, FormStateInterface $form_state) {
       '#type' => 'select',
       '#title' => $this->t('Timezone'),
       '#description' => $this->t('Timezone to be used for date output.'),
-      '#options' => ['' => $this->t('- Default site/user timezone -')] + system_time_zones(FALSE, TRUE),
+      '#options' => ['' => $this->t('- Default site/user timezone -')] + system_time_zones(FALSE),
       '#default_value' => $this->options['timezone'],
     ];
     foreach (array_merge(['custom'], array_keys($date_formats)) as $timezone_date_formats) {