diff --git a/core/includes/form.inc b/core/includes/form.inc
index c1f5620..d2cfd47 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -371,7 +371,21 @@ function template_preprocess_form(&$variables) {
     if (!empty($error_links)) {
       // We need to pass this through String::format() so drupal_set_message()
       // doesn't encode the links.
-      $message =  \Drupal::translation()->formatPlural(count($error_links), '1 error has been found', '@count errors have been found') . ': ' . implode(', ', $error_links);
+      $error_count = count($error_links);
+      $last_error_link = array_pop($error_links);
+      $starting_error_links = implode(', ', $error_links);
+      if ($error_count > 2) {
+        // The style guide requires a serial comma.
+        $starting_error_links .= ',';
+      }
+      $message =  \Drupal::translation()->formatPlural($error_count,
+        '1 error has been found: !last_error_link.',
+        '@count errors have been found: !starting_error_links and !last_error_link.',
+        [
+          '!starting_error_links' => $starting_error_links,
+          '!last_error_link' => $last_error_link,
+        ]
+      );
       $message = String::format($message, $error_titles);
       drupal_set_message($message, 'error');
     }
diff --git a/core/modules/system/css/system.theme.css b/core/modules/system/css/system.theme.css
index ea40f4c..0503df4 100644
--- a/core/modules/system/css/system.theme.css
+++ b/core/modules/system/css/system.theme.css
@@ -113,11 +113,17 @@ abbr.ajax-changed {
   margin-right: 0;
 }
 
+.form-error {
+  background-color: #fef5f1;
+  border: 1px solid #ed541d;
+  color: #8c2e0b;
+  padding: 5px;
+}
 .form-error-message {
   margin-bottom: 10px;
   min-height: 25px;
 }
-.form-error .fieldset-legend {
+.form-error legend {
   position: absolute;
 }
 .form-error .fieldset-wrapper {