diff -u b/core/modules/system/templates/admin-block-content.html.twig b/core/modules/system/templates/admin-block-content.html.twig
--- b/core/modules/system/templates/admin-block-content.html.twig
+++ b/core/modules/system/templates/admin-block-content.html.twig
@@ -9,7 +9,7 @@
  *   contain the keys 'title', 'link_path', and 'localized_options', which are
  *   passed to l(). A 'description' key may also be provided.
  * - attributes: HTML attributes to be added to the element.
- * - compact: This is true, if compact mode is turned on.
+ * - compact: True if compact mode is turned on.
  *
  * @see template_preprocess_admin_block_content()
  *
diff -u b/core/modules/system/templates/status-report.html.twig b/core/modules/system/templates/status-report.html.twig
--- b/core/modules/system/templates/status-report.html.twig
+++ b/core/modules/system/templates/status-report.html.twig
@@ -10,26 +10,13 @@
  *   - value: (optional) The requirement's status.
  *   - description: (optional) The requirement's description.
  *   - severity_title: The title of the severity.
- *   - severity_status: Indicates the severity status. This can be:
- *     * info
- *     * ok
- *     * warning
- *     * error
+ *   - severity_status: Indicates the severity status.
  *
  * @see template_preprocess_status_report()
  *
  * @ingroup themeable
  */
 #}
-{# severity_status : class #}
-{%
-  set severities = {
-    'info' : 'info',
-    'ok' : 'ok',
-    'warning' : 'warning',
-    'error' : 'error',
-  }
-%}
 <table class="system-status-report">
   <thead>
     <tr class="visually-hidden">
@@ -38,7 +25,7 @@
   </thead>
   <tbody>
   {% for requirement in requirements %}
-    <tr class="{{ severities[requirement.severity_status] }}">
+    <tr class="{{ severity_status|clean_class }}">
       <td class="status-icon">
         <div title="{{ requirement.severity_title }}">
           <span class="visually-hidden">{{ requirement.severity_title }}</span>
diff -u b/core/modules/system/templates/system-themes-page.html.twig b/core/modules/system/templates/system-themes-page.html.twig
--- b/core/modules/system/templates/system-themes-page.html.twig
+++ b/core/modules/system/templates/system-themes-page.html.twig
@@ -33,11 +33,11 @@
     {%
       set theme_group_classes = [
         'system-themes-list',
-        'system-themes-list-' ~ theme_group.state|clean_class,
+        'system-themes-list-' ~ theme_group.state,
         'clearfix',
       ]
     %}
-    <div {{ theme_group.attributes.addClass(theme_group_classes) }}>
+    <div{{ theme_group.attributes.addClass(theme_group_classes) }}>
       <h2>{{ theme_group.title }}</h2>
       {% for theme in theme_group.themes %}
         {%
diff -u b/core/themes/seven/templates/admin-block-content.html.twig b/core/themes/seven/templates/admin-block-content.html.twig
--- b/core/themes/seven/templates/admin-block-content.html.twig
+++ b/core/themes/seven/templates/admin-block-content.html.twig
@@ -11,7 +11,7 @@
  *   - title: Short name of the section.
  *   - description: Description of the administrative menu item.
  * - attributes: HTML attributes to be added to the element.
- * - compact: This is true, if compact mode is turned on.
+ * - compact: This is true if compact mode is turned on.
  *
  * @see template_preprocess_admin_block_content()
  * @see seven_preprocess_admin_block_content()