diff -u b/core/modules/system/src/Form/ModulesListForm.php b/core/modules/system/src/Form/ModulesListForm.php
--- b/core/modules/system/src/Form/ModulesListForm.php
+++ b/core/modules/system/src/Form/ModulesListForm.php
@@ -235,7 +235,7 @@
     // Lastly, sort all packages by title.
     uasort($form['modules'], array('\Drupal\Component\Utility\SortArray', 'sortByTitleProperty'));
 
-    $form['#attributes']['class'] = array('system-modules', 'system-projects');
+    $form['#attributes']['class'] = ['system-modules', 'system-projects'];
     $form['#attached']['library'][] = 'system/drupal.system.modules';
     $form['actions'] = array('#type' => 'actions');
     $form['actions']['submit'] = array(
diff -u b/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
--- b/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -371,7 +371,7 @@
   $groups = array();
   $theme_groups = $variables['theme_groups'];
   $variables['attributes']['id'] = 'system-themes-page';
-  $variables['attributes']['class'] = array('system-themes', 'system-projects');
+  $variables['attributes']['class'] = ['system-themes', 'system-projects'];
   $theme_infos = array();
 
   // Build a list of theme names for all known themes
@@ -417,28 +417,24 @@
       }
 
       $version = isset($theme->info['version']) ? $theme->info['version'] : '';
-      // Add the description, along with any theme it requires.
-      $description = '';
-      $description .= '<div class="requirements">';
-      $description .= '<div class="admin-requirements">' . t('Machine name: !machine-name', array('!machine-name' => '<span dir="ltr" class="table-filter-text-source">' . $theme->getName() . '</span>')) . '</div>';
-      if ($version) {
-        $description .= '<div class="admin-requirements">' . t('Version: !module-version', array('!module-version' => $version)) . '</div>';
-      }
-      if (!empty($theme->requires)) {
-        $names = array();
-        foreach (array_keys($theme->requires) as $key) {
-          $names[] = isset($theme_infos[$key]) ? $theme_infos[$key] : $key;
-        }
-        $description .= '<div class="admin-requirements">' . t('Requires: !module-list', array('!module-list' => implode(', ', $names))) . '</div>';
+
+      $requires = [];
+      foreach (array_keys($theme->requires) as $key) {
+        $requires[$key] = isset($theme_infos[$key]) ? $theme_infos[$key] : $key;
       }
-      if (!empty($theme->required_by)) {
-        $names = array();
-        foreach (array_keys($theme->required_by) as $key) {
-          $names[] = isset($theme_infos[$key]) ? $theme_infos[$key] : $key;
-        }
-        $description .= '<div class="admin-requirements">' . t('Required by: !module-list', array('!module-list' => implode(', ', $names))) . '</div>';
+
+      $required_by = [];
+      foreach (array_keys($theme->required_by) as $key) {
+        $required_by[$key] = isset($theme_infos[$key]) ? $theme_infos[$key] : $key;
       }
-      $description .= '</div>';
+
+     $description = [
+        '#theme' => 'system_project_details__theme',
+        '#machine_name' => $theme->getName(),
+        '#version' => $version,
+        '#requires' => $requires,
+        '#required_by' => $required_by,
+      ];
 
       // Localize the theme description.
       $current_theme['description'] = array(
@@ -492 +487,0 @@
-
only in patch2:
unchanged:
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -217,6 +217,14 @@ function system_theme() {
       'variables' => array('menu_items' => NULL),
       'file' => 'system.admin.inc',
     ),
+    'system_project_details' => [
+      'variables' => [
+        'machine_name' => [],
+        'version' => '',
+        'requires' => [],
+        'required_by' => [],
+      ],
+    ],
   ));
 }
 
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/templates/system-project-details.html.twig
@@ -0,0 +1,22 @@
+
+{#
+/**
+ * @file
+ * Default theme implementation for the Project details.
+ *
+ * Available variables:
+ * - attributes: HTML attributes for the main container.
+ * - machine_name: The machine name of the project.
+ * - requires: The names of projects required by this project.
+ * - required_by: The projects that are requires this project.
+ *
+ * @ingroup themeable
+ */
+#}
+<div{{ attributes }}>
+  <div>{{ machine_name }}</div>
+  <div>{{ version }}</div>
+  <div>{{ 'Requires: @extensions'|t({'@extensions': requires|join(', ')}) }}</div>
+  <div>{{ 'Required by: @extensions'|t({'@extensions': required_by|join(', ')}) }}</div>
+</div>
+
only in patch2:
unchanged:
--- /dev/null
+++ b/core/themes/classy/templates/misc/system-project-details.html.twig
@@ -0,0 +1,22 @@
+
+{#
+/**
+ * @file
+ * Theme override for the Project details.
+ *
+ * Available variables:
+ * - attributes: HTML attributes for the main container.
+ * - machine_name: The machine name of the project.
+ * - requires: The names of projects required by this project.
+ * - required_by: The projects that are requires this project.
+ *
+ * @ingroup themeable
+ */
+#}
+<div{{ attributes.addClass('project-details') }}>
+  <div class="details">{{ machine_name }}</div>
+  <div class="details">{{ version }}</div>
+  <div class="details">{{ 'Requires: @extensions'|t({'@extensions': requires|join(', ')}) }}</div>
+  <div class="details">{{ 'Required by: @extensions'|t({'@extensions': required_by|join(', ')}) }}</div>
+</div>
+