diff --git b/core/includes/theme.inc a/core/includes/theme.inc
index ae88d19..2aef832c 100644
--- b/core/includes/theme.inc
+++ a/core/includes/theme.inc
@@ -549,7 +549,7 @@ function template_preprocess_datetime_wrapper(&$variables) {
  * list items differently when the link is active, since CSS does not yet allow
  * one to style list items only if it contains a certain element with a certain
  * class. I.e. we cannot yet convert this jQuery selector to a CSS selector:
- *   jQuery('li:has("a.active")')
+ *   jQuery('li:has("a.is-active")')
  *
  * @see \Drupal\Core\Utility\LinkGenerator
  * @see \Drupal\Core\Utility\LinkGenerator::generate()
diff --git b/core/modules/toolbar/css/toolbar.menu.css a/core/modules/toolbar/css/toolbar.menu.css
index 09a4135..14dbd44 100644
--- b/core/modules/toolbar/css/toolbar.menu.css
+++ a/core/modules/toolbar/css/toolbar.menu.css
@@ -36,7 +36,7 @@
 
 /* ----- Toolbar menu tray for viewports less than 320px ------ */
 @media screen and (max-width: 319px) {
-  .toolbar .toolbar-tray-vertical.active {
+  .toolbar .toolbar-tray-vertical.is-active {
     width: 100%;
   }
 }
diff --git b/core/modules/views/templates/views-view-summary-unformatted.html.twig a/core/modules/views/templates/views-view-summary-unformatted.html.twig
index 57a6e83..df90d40 100644
--- b/core/modules/views/templates/views-view-summary-unformatted.html.twig
+++ a/core/modules/views/templates/views-view-summary-unformatted.html.twig
@@ -25,7 +25,7 @@
   {% if row.separator -%}
     {{ row.separator }}
   {%- endif %}
-  <a href="{{ row.url }}"{{ row.attributes.addClass(row.active ? 'active') }}>{{ row.link }}</a>
+  <a href="{{ row.url }}"{{ row.attributes.addClass(row.active ? 'is-active') }}>{{ row.link }}</a>
   {% if options.count %}
     ({{ row.count }})
   {% endif %}
diff --git b/core/modules/views/templates/views-view-summary.html.twig a/core/modules/views/templates/views-view-summary.html.twig
index f1e788b..86b78ad 100644
--- b/core/modules/views/templates/views-view-summary.html.twig
+++ a/core/modules/views/templates/views-view-summary.html.twig
@@ -23,7 +23,7 @@
 <div class="item-list">
   <ul class="views-summary">
   {% for row in rows %}
-    <li><a href="{{ row.url }}"{{ row.attributes.addClass(row.active ? 'active') }}>{{ row.link }}</a>
+    <li><a href="{{ row.url }}"{{ row.attributes.addClass(row.active ? 'is-active') }}>{{ row.link }}</a>
       {% if options.count %}
         ({{ row.count }})
       {% endif %}
diff --git b/core/themes/bartik/css/components/primary-menu.css a/core/themes/bartik/css/components/primary-menu.css
index ac1e681..8b68e85 100644
--- b/core/themes/bartik/css/components/primary-menu.css
+++ a/core/themes/bartik/css/components/primary-menu.css
@@ -182,7 +182,7 @@ body:not(:target) .region-primary-menu .menu-toggle-target-show:target ~ .menu .
     padding: 0.7em 0.8em;
   }
   .featured .region-primary-menu .menu-item a:active,
-  .featured .region-primary-menu .menu-item a.active {
+  .featured .region-primary-menu .menu-item a.is-active {
     background: #f0f0f0;
     background: rgba(240, 240, 240, 1.0);
   }
diff --git b/core/themes/bartik/css/components/site-footer.css a/core/themes/bartik/css/components/site-footer.css
index b0c8814..9ed78ab 100644
--- b/core/themes/bartik/css/components/site-footer.css
+++ a/core/themes/bartik/css/components/site-footer.css
@@ -57,7 +57,7 @@
   padding-left: 0;
 }
 .site-footer .content a,
-.site-footer .content a.active {
+.site-footer .content a.is-active {
   color: #fcfcfc;
   color: rgba(255, 255, 255, 0.8);
 }
diff --git b/core/themes/classy/templates/dataset/table.html.twig a/core/themes/classy/templates/dataset/table.html.twig
index 518c10c..f8e6a6c 100644
--- b/core/themes/classy/templates/dataset/table.html.twig
+++ a/core/themes/classy/templates/dataset/table.html.twig
@@ -62,7 +62,7 @@
         {% for cell in header %}
           {%
             set cell_classes = [
-              cell.active_table_sort ? 'active',
+              cell.active_table_sort ? 'is-active',
             ]
           %}
           <{{ cell.tag }}{{ cell.attributes.addClass(cell_classes) }}>