diff --git a/core/modules/views/templates/views-view-summary.html.twig b/core/modules/views/templates/views-view-summary.html.twig
new file mode 100644
index 0000000..227c3ce
--- /dev/null
+++ b/core/modules/views/templates/views-view-summary.html.twig
@@ -0,0 +1,32 @@
+{#
+/**
+ * @file
+ * Default theme implementation to display a list of summary lines.
+ *
+ * Available variables:
+ * - rows: The rows contained in this view.
+ *   Each row contains:
+ *   - url: The summary link URL.
+ *   - link: The summary link text.
+ *   - count: The number of items under this grouping.
+ * - row_classes: HTML classes to apply to each row, indexed by row ID.
+ *   This matches the index in rows.
+ * - options.count: A views option for whether to show the count.
+ *
+ * @see template_preprocess()
+ * @see template_preprocess_views_view_summary()
+ *
+ * @ingroup themeable
+ */
+#}
+<div class="item-list">
+  <ul class="views-summary">
+  {% for id, row in rows %}
+    <li><a href="{{ row.url }}"{{ row_classes[id] }}>{{ row.link }}</a>
+      {% if options.count %}
+        ({{ row.count }})
+      {% endif %}
+    </li>
+  {% endfor %}
+  </ul>
+</div>
diff --git a/core/modules/views/templates/views-view-summary.tpl.php b/core/modules/views/templates/views-view-summary.tpl.php
deleted file mode 100644
index ce51e70..0000000
--- a/core/modules/views/templates/views-view-summary.tpl.php
+++ /dev/null
@@ -1,20 +0,0 @@
-<?php
-
-/**
- * @file
- * Default simple view template to display a list of summary lines.
- *
- * @ingroup views_templates
- */
-?>
-<div class="item-list">
-  <ul class="views-summary">
-  <?php foreach ($rows as $id => $row): ?>
-    <li><a href="<?php print $row->url; ?>"<?php print $row_classes[$id]; ?>><?php print $row->link; ?></a>
-      <?php if (!empty($options['count'])): ?>
-        (<?php print $row->count?>)
-      <?php endif; ?>
-    </li>
-  <?php endforeach; ?>
-  </ul>
-</div>
diff --git a/core/modules/views/views.theme.inc b/core/modules/views/views.theme.inc
index e0bbbeb..9ab294b 100644
--- a/core/modules/views/views.theme.inc
+++ b/core/modules/views/views.theme.inc
@@ -328,10 +328,19 @@ function template_preprocess_views_view_field(&$vars) {
 }
 
 /**
- * Preprocess theme function to print a single record from a row, with fields
+ * Prepares variables for views summary templates.
+ *
+ * The summary prints a single record from a row, with fields.
+ *
+ * Default template: views-view-summary.html.twig.
+ *
+ * @param array $vars
+ *   An associative array containing:
+ *   - view: A ViewExecutable object.
+ *   - rows: The raw row data.
  */
 function template_preprocess_views_view_summary(&$vars) {
-  $view     = $vars['view'];
+  $view = $vars['view'];
   $argument = $view->argument[$view->build_info['summary_level']];
   $vars['row_classes'] = array();
 
@@ -346,8 +355,9 @@ function template_preprocess_views_view_summary(&$vars) {
     url(current_path()), // could be an alias
   ));
 
-  // Collect all arguments foreach row, to be able to alter them for example by the validator.
-  // This is not done per single argument value, because this could cause performance problems.
+  // Collect all arguments foreach row, to be able to alter them for example
+  // by the validator. This is not done per single argument value, because this
+  // could cause performance problems.
   $row_args = array();
 
   foreach ($vars['rows'] as $id => $row) {
@@ -356,7 +366,6 @@ function template_preprocess_views_view_summary(&$vars) {
   $argument->process_summary_arguments($row_args);
 
   foreach ($vars['rows'] as $id => $row) {
-
     $vars['rows'][$id]->link = $argument->summary_name($row);
     $args = $view->args;
     $args[$argument->position] = $row_args[$id];
@@ -367,7 +376,6 @@ function template_preprocess_views_view_summary(&$vars) {
     }
     $vars['rows'][$id]->url = url($view->getUrl($args, $base_path), $url_options);
     $vars['rows'][$id]->count = intval($row->{$argument->count_alias});
-
     $vars['row_classes'][$id] = array();
     if (isset($active_urls[$vars['rows'][$id]->url])) {
       $vars['row_classes'][$id]['class'][] = 'active';