diff --git a/core/modules/contextual/css/contextual.icons.css b/core/modules/contextual/css/contextual.icons.css
index 2a755ca..1e456a3 100644
--- a/core/modules/contextual/css/contextual.icons.css
+++ b/core/modules/contextual/css/contextual.icons.css
@@ -13,11 +13,11 @@
   background-image: url("../../../misc/icons/bebebe/pencil.png");
 }
 .toolbar-bar .toolbar-icon-edit:active:before,
-.toolbar-bar .toolbar-icon-edit.active:before {
+.toolbar-bar .toolbar-icon-edit.is-active:before {
   background-image: url("../../../misc/icons/ffffff/pencil.svg");
 }
 .no-svg .toolbar-bar .toolbar-icon-edit:active:before,
-.no-svg .toolbar-bar .toolbar-icon-edit.active:before {
+.no-svg .toolbar-bar .toolbar-icon-edit.is-active:before {
   background-image: url("../../../misc/icons/ffffff/pencil.png");
 }
 
diff --git a/core/modules/shortcut/css/shortcut.icons.css b/core/modules/shortcut/css/shortcut.icons.css
index 143b115..6a85a2e 100644
--- a/core/modules/shortcut/css/shortcut.icons.css
+++ b/core/modules/shortcut/css/shortcut.icons.css
@@ -13,11 +13,11 @@
   background-image: url("../../../misc/icons/bebebe/star.png");
 }
 .toolbar-bar .toolbar-icon-shortcut:active:before,
-.toolbar-bar .toolbar-icon-shortcut.active:before {
+.toolbar-bar .toolbar-icon-shortcut.is-active:before {
   background-image: url("../../../misc/icons/ffffff/star.svg");
 }
 .no-svg .toolbar-bar .toolbar-icon-shortcut:active:before,
-.no-svg .toolbar-bar .toolbar-icon-shortcut.active:before {
+.no-svg .toolbar-bar .toolbar-icon-shortcut.is-active:before {
   background-image: url("../../../misc/icons/ffffff/star.png");
 }
 
diff --git a/core/modules/toolbar/css/toolbar.icons.css b/core/modules/toolbar/css/toolbar.icons.css
index 7bcdf65..68f780a 100644
--- a/core/modules/toolbar/css/toolbar.icons.css
+++ b/core/modules/toolbar/css/toolbar.icons.css
@@ -72,11 +72,11 @@
   background-image: url("../../../misc/icons/bebebe/hamburger.png");
 }
 .toolbar-bar .toolbar-icon-menu:active:before,
-.toolbar-bar .toolbar-icon-menu.active:before {
+.toolbar-bar .toolbar-icon-menu.is-active:before {
   background-image: url("../../../misc/icons/ffffff/hamburger.svg");
 }
 .no-svg .toolbar-bar .toolbar-icon-menu:active:before,
-.no-svg .toolbar-bar .toolbar-icon-menu.active:before {
+.no-svg .toolbar-bar .toolbar-icon-menu.is-active:before {
   background-image: url("../../../misc/icons/ffffff/hamburger.png");
 }
 .toolbar-bar .toolbar-icon-help:before {
@@ -86,11 +86,11 @@
   background-image: url("../../../misc/icons/bebebe/questionmark-disc.png");
 }
 .toolbar-bar .toolbar-icon-help:active:before,
-.toolbar-bar .toolbar-icon-help.active:before {
+.toolbar-bar .toolbar-icon-help.is-active:before {
   background-image: url("../../../misc/icons/ffffff/questionmark-disc.svg");
 }
 .no-svg .toolbar-bar .toolbar-icon-help:active:before,
-.no-svg .toolbar-bar .toolbar-icon-help.active:before {
+.no-svg .toolbar-bar .toolbar-icon-help.is-active:before {
   background-image: url("../../../misc/icons/ffffff/questionmark-disc.png");
 }
 
@@ -104,11 +104,11 @@
   background-image: url("../../../misc/icons/787878/file.png");
 }
 .toolbar-icon-content:active:before,
-.toolbar-icon-content.active:before {
+.toolbar-icon-content.is-active:before {
   background-image: url("../../../misc/icons/000000/file.svg");
 }
 .no-svg .toolbar-icon-content:active:before,
-.no-svg .toolbar-icon-content.active:before {
+.no-svg .toolbar-icon-content.is-active:before {
   background-image: url("../../../misc/icons/000000/file.png");
 }
 .toolbar-icon-structure:before {
@@ -118,11 +118,11 @@
   background-image: url("../../../misc/icons/787878/orgchart.png");
 }
 .toolbar-icon-structure:active:before,
-.toolbar-icon-structure.active:before {
+.toolbar-icon-structure.is-active:before {
   background-image: url("../../../misc/icons/000000/orgchart.svg");
 }
 .no-svg .toolbar-icon-structure:active:before,
-.no-svg .toolbar-icon-structure.active:before {
+.no-svg .toolbar-icon-structure.is-active:before {
   background-image: url("../../../misc/icons/000000/orgchart.png");
 }
 .toolbar-icon-appearance:before {
@@ -132,11 +132,11 @@
   background-image: url("../../../misc/icons/787878/paintbrush.png");
 }
 .toolbar-icon-appearance:active:before,
-.toolbar-icon-appearance.active:before {
+.toolbar-icon-appearance.is-active:before {
   background-image: url("../../../misc/icons/000000/paintbrush.svg");
 }
 .no-svg .toolbar-icon-appearance:active:before,
-.no-svg .toolbar-icon-appearance.active:before {
+.no-svg .toolbar-icon-appearance.is-active:before {
   background-image: url("../../../misc/icons/000000/paintbrush.png");
 }
 .toolbar-icon-people:before {
@@ -146,11 +146,11 @@
   background-image: url("../../../misc/icons/787878/people.png");
 }
 .toolbar-icon-people:active:before,
-.toolbar-icon-people.active:before {
+.toolbar-icon-people.is-active:before {
   background-image: url("../../../misc/icons/000000/people.svg");
 }
 .no-svg .toolbar-icon-people:active:before,
-.no-svg .toolbar-icon-people.active:before {
+.no-svg .toolbar-icon-people.is-active:before {
   background-image: url("../../../misc/icons/000000/people.png");
 }
 .toolbar-icon-extend:before {
@@ -160,11 +160,11 @@
   background-image: url("../../../misc/icons/787878/puzzlepiece.png");
 }
 .toolbar-icon-extend:active:before,
-.toolbar-icon-extend.active:before {
+.toolbar-icon-extend.is-active:before {
   background-image: url("../../../misc/icons/000000/puzzlepiece.svg");
 }
 .no-svg .toolbar-icon-extend:active:before,
-.no-svg .toolbar-icon-extend.active:before {
+.no-svg .toolbar-icon-extend.is-active:before {
   background-image: url("../../../misc/icons/000000/puzzlepiece.png");
 }
 .toolbar-icon-configuration:before {
@@ -174,11 +174,11 @@
   background-image: url("../../../misc/icons/787878/wrench.png");
 }
 .toolbar-icon-configuration:active:before,
-.toolbar-icon-configuration.active:before {
+.toolbar-icon-configuration.is-active:before {
   background-image: url("../../../misc/icons/000000/wrench.svg");
 }
 .no-svg .toolbar-icon-configuration:active:before,
-.no-svg .toolbar-icon-configuration.active:before {
+.no-svg .toolbar-icon-configuration.is-active:before {
   background-image: url("../../../misc/icons/000000/wrench.png");
 }
 .toolbar-icon-reports:before {
@@ -188,11 +188,11 @@
   background-image: url("../../../misc/icons/787878/barchart.png");
 }
 .toolbar-icon-reports:active:before,
-.toolbar-icon-reports.active:before {
+.toolbar-icon-reports.is-active:before {
   background-image: url("../../../misc/icons/000000/barchart.svg");
 }
 .no-svg .toolbar-icon-reports:active:before,
-.no-svg .toolbar-icon-reports.active:before {
+.no-svg .toolbar-icon-reports.is-active:before {
   background-image: url("../../../misc/icons/000000/barchart.png");
 }
 .toolbar-icon-help:before {
@@ -202,11 +202,11 @@
   background-image: url("../../../misc/icons/787878/questionmark-disc.png");
 }
 .toolbar-icon-help:active:before,
-.toolbar-icon-help.active:before {
+.toolbar-icon-help.is-active:before {
   background-image: url("../../../misc/icons/000000/questionmark-disc.svg");
 }
 .no-svg .toolbar-icon-help:active:before,
-.no-svg .toolbar-icon-help.active:before {
+.no-svg .toolbar-icon-help.is-active:before {
   background-image: url("../../../misc/icons/000000/questionmark-disc.png");
 }
 
@@ -367,4 +367,3 @@
 .no-svg .toolbar .toolbar-toggle-orientation [value="horizontal"]:hover:before {
   background-image: url("../../../misc/icons/787878/push-up.png");
 }
-
diff --git a/core/modules/toolbar/css/toolbar.theme.css b/core/modules/toolbar/css/toolbar.theme.css
index 5a585d2..fb7dbdf 100644
--- a/core/modules/toolbar/css/toolbar.theme.css
+++ b/core/modules/toolbar/css/toolbar.theme.css
@@ -46,7 +46,7 @@
   background-image: linear-gradient(rgba(255, 255, 255, 0.125) 20%, transparent 200%);
   text-decoration: none;
 }
-.toolbar .toolbar-bar .toolbar-tab > .toolbar-item.active {
+.toolbar .toolbar-bar .toolbar-tab > .toolbar-item.is-active {
   background-image: -webkit-linear-gradient(rgba(255, 255, 255, 0.25) 20%, transparent 200%);
   background-image: linear-gradient(rgba(255, 255, 255, 0.25) 20%, transparent 200%);
 }
@@ -92,7 +92,7 @@
 }
 .toolbar-tray a:hover,
 .toolbar-tray a:active,
-.toolbar-tray a.active {
+.toolbar-tray a.is-active {
   color: #000;
   text-decoration: underline;
 }
diff --git a/core/modules/user/css/user.icons.css b/core/modules/user/css/user.icons.css
index e61128c..aa09bcc 100644
--- a/core/modules/user/css/user.icons.css
+++ b/core/modules/user/css/user.icons.css
@@ -13,10 +13,10 @@
   background-image: url("../../../misc/icons/bebebe/person.png");
 }
 .toolbar-bar .toolbar-icon-user:active:before,
-.toolbar-bar .toolbar-icon-user.active:before {
+.toolbar-bar .toolbar-icon-user.is-active:before {
   background-image: url("../../../misc/icons/ffffff/person.svg");
 }
 .no-svg .toolbar-bar .toolbar-icon-user:active:before,
-.no-svg .toolbar-bar .toolbar-icon-user.active:before {
+.no-svg .toolbar-bar .toolbar-icon-user.is-active:before {
   background-image: url("../../../misc/icons/ffffff/person.png");
 }
diff --git a/core/themes/bartik/color/preview.css b/core/themes/bartik/color/preview.css
index 65e9ad7..10b6022 100644
--- a/core/themes/bartik/color/preview.css
+++ b/core/themes/bartik/color/preview.css
@@ -59,7 +59,7 @@
   background: #b3b3b3;
   background: rgba(255, 255, 255, 1);
 }
-#preview-main-menu-links li a.active {
+#preview-main-menu-links li a.is-active {
   border-bottom: none;
 }
 #preview-main-menu-links li {
diff --git a/core/themes/seven/js/mobile.install.js b/core/themes/seven/js/mobile.install.js
index 28268bf..1b103bb 100644
--- a/core/themes/seven/js/mobile.install.js
+++ b/core/themes/seven/js/mobile.install.js
@@ -4,7 +4,7 @@
 
   function findActiveStep (steps) {
     for (var i = 0; i < steps.length; i++) {
-      if (steps[i].className === 'active') {
+      if (steps[i].className === 'is-active') {
         return i + 1;
       }
     }
diff --git a/core/themes/seven/maintenance-page.css b/core/themes/seven/maintenance-page.css
index bc56fa0..5e83d72 100644
--- a/core/themes/seven/maintenance-page.css
+++ b/core/themes/seven/maintenance-page.css
@@ -69,12 +69,12 @@
   [dir="rtl"] .task-list li {
     padding: 0.5em 1em 0.5em 1em;
   }
-  .task-list .active {
+  .task-list .is-active {
     background: #ebeae4;
     position: relative;
     font-weight: normal;
   }
-  .task-list .active:after {
+  .task-list .is-active:after {
     left: 100%; /* LTR */
     border: solid transparent;
     border-color: rgba(235, 234, 228, 0);
@@ -88,7 +88,7 @@
     top: 50%;
     margin-top: -1.32em;
   }
-  [dir="rtl"] .task-list .active:after {
+  [dir="rtl"] .task-list .is-active:after {
     left: auto;
     right: 100%;
     border-left-color: transparent;
diff --git a/core/themes/seven/style.css b/core/themes/seven/style.css
index 33b3eee..80a2e88 100644
--- a/core/themes/seven/style.css
+++ b/core/themes/seven/style.css
@@ -214,7 +214,7 @@ li.tabs__tab a {
   margin: 16px 0 0;
   margin: 1rem 0 0;
 }
-.tabs.primary .tabs__tab.active {
+.tabs.primary .tabs__tab.is-active {
   z-index: 15;
   border-color: #a6a6a6;
   border-radius: 4px 0 0 0;
@@ -229,7 +229,7 @@ li.tabs__tab a {
   background-color: #fafaf7;
   text-decoration: underline;
 }
-.tabs.primary .active a:focus {
+.tabs.primary .is-active a:focus {
   background: none;
   text-decoration: underline;
 }
@@ -248,7 +248,7 @@ li.tabs__tab a {
   [dir="rtl"] .no-svg .tabs.primary a {
     background-image: url(../../misc/icons/0074bd/chevron-left.png);
   }
-  .tabs.primary .tabs__tab.active a {
+  .tabs.primary .tabs__tab.is-active a {
     background-image: none;
   }
 }
@@ -295,21 +295,21 @@ li.tabs__tab a {
   padding-bottom:16px;
   padding-bottom: 1rem;
 }
-.is-collapse-enabled .tabs__tab.active {
+.is-collapse-enabled .tabs__tab.is-active {
   position: absolute;
   top: 2px;
   left: 0;
   width: 75%;
   border-bottom: 0;
 }
-[dir="rtl"] .is-collapse-enabled .tabs__tab.active {
+[dir="rtl"] .is-collapse-enabled .tabs__tab.is-active {
   left: auto;
   right: 0;
 }
-.is-collapse-enabled .tabs.primary a.active:before {
+.is-collapse-enabled .tabs.primary a.is-active:before {
   content: none;
 }
-.is-open .tabs__tab.active {
+.is-open .tabs__tab.is-active {
   border-color: #a6a6a6;
   background-color: #ffffff;
   color: #004f80;
@@ -350,9 +350,9 @@ li.tabs__tab a {
 }
 
 /* Override the states above */
-.is-horizontal .tabs__tab.active,
-.is-horizontal .tabs.primary .tabs__tab.active,
-[dir="rtl"] .is-horizontal .tabs.primary .tabs__tab.active {
+.is-horizontal .tabs__tab.is-active,
+.is-horizontal .tabs.primary .tabs__tab.is-active,
+[dir="rtl"] .is-horizontal .tabs.primary .tabs__tab.is-active {
   border-radius: 4px 4px 0 0;
   position: relative;
   width: auto;
@@ -360,7 +360,7 @@ li.tabs__tab a {
   border-bottom: 0;
   margin: 0 -4px;
 }
-[dir="rtl"] .is-horizontal .tabs__tab.active {
+[dir="rtl"] .is-horizontal .tabs__tab.is-active {
   margin: 0 -6px;
 }
 .is-horizontal .tabs.primary a {
@@ -389,7 +389,7 @@ li.tabs__tab a {
 .tabs.secondary .tabs__tab + .tabs__tab {
   border-top: 1px solid #d9d8d4;
 }
-.tabs.secondary .tabs__tab.active {
+.tabs.secondary .tabs__tab.is-active {
   color: #004f80;
   border-left: 2px solid #004f80;
   padding-left: 15px;
@@ -404,7 +404,7 @@ li.tabs__tab a {
   padding: 7px 13px 5px;
   text-decoration: none;
 }
-.tabs.secondary .active a {
+.tabs.secondary .is-active a {
   color: #004f80;
 }
 .tabs.secondary a:focus {
@@ -426,7 +426,7 @@ li.tabs__tab a {
   border-top: 0;
   padding: 0;
 }
-.is-horizontal .tabs.secondary .tabs__tab.active {
+.is-horizontal .tabs.secondary .tabs__tab.is-active {
   border-bottom-color: #004f80;
 }
 .is-horizontal .tabs.secondary .tabs__tab:hover {
@@ -631,38 +631,38 @@ th > a:after {
   border-bottom: 2px solid transparent;
   transition: all 0.1s;
 }
-th.active > a {
+th.is-active > a {
   color: #004875;
 }
-th.active img {
+th.is-active img {
   position: absolute;
   right: 0; /* LTR */
   top: 50%;
 }
-[dir="rtl"] th.active img {
+[dir="rtl"] th.is-active img {
   right: auto;
   left: 0;
 }
-th.active > a:after {
+th.is-active > a:after {
   border-bottom-color: #004875;
 }
 th > a:focus,
 th > a:hover,
-th.active > a:focus,
-th.active > a:hover {
+th.is-active > a:focus,
+th.is-active > a:hover {
   color: #008ee6;
   text-decoration: none;
 }
 th > a:focus:after,
 th > a:hover:after,
-th.active > a:focus:after,
-th.active > a:hover:after {
+th.is-active > a:focus:after,
+th.is-active > a:hover:after {
   border-bottom-color: #008ee6;
 }
 td .item-list ul {
   margin: 0;
 }
-td.active {
+td.is-active {
   background: none;
 }
 
@@ -1217,8 +1217,8 @@ details.fieldset-no-legend {
 }
 
 .views-displays ul.secondary li a,
-.views-displays ul.secondary li.active a,
-.views-displays ul.secondary li.active a.active {
+.views-displays ul.secondary li.is-active a,
+.views-displays ul.secondary li.is-active a.is-active {
   padding: 2px 7px 3px;
 }
 
@@ -1226,8 +1226,8 @@ details.fieldset-no-legend {
   color: #0074bd;
 }
 
-.views-displays ul.secondary li.active a,
-.views-displays ul.secondary li.active a.active {
+.views-displays ul.secondary li.is-active a,
+.views-displays ul.secondary li.is-active a.is-active {
   border: 1px solid transparent;
 }