diff --git a/core/modules/system/templates/install-page.html.twig b/core/modules/system/templates/install-page.html.twig
index ad1c04c..24d17fa 100644
--- a/core/modules/system/templates/install-page.html.twig
+++ b/core/modules/system/templates/install-page.html.twig
@@ -11,7 +11,7 @@
  * @ingroup themeable
  */
 #}
-  <div class="l-container">
+  <div class="layout-container">
 
     <header role="banner">
       {% if site_name or site_slogan %}
@@ -35,15 +35,15 @@
     </main>
 
     {% if page.sidebar_first %}
-      <aside class="l-sidebar-first" role="complementary">
+      <aside class="layout-sidebar-first" role="complementary">
         {{ page.sidebar_first }}
-      </aside>{# /.l-sidebar-first #}
+      </aside>{# /.layout-sidebar-first #}
     {% endif %}
 
     {% if page.sidebar_second %}
-      <aside class="l-sidebar-second" role="complementary">
+      <aside class="layout-sidebar-second" role="complementary">
         {{ page.sidebar_second }}
-      </aside>{# /.l-sidebar-second #}
+      </aside>{# /.layout-sidebar-second #}
     {% endif %}
 
     {% if page.footer %}
@@ -52,4 +52,4 @@
       </footer>
     {% endif %}
 
-  </div>{# /.l-container #}
+  </div>{# /.layout-container #}
diff --git a/core/themes/seven/maintenance-page.css b/core/themes/seven/maintenance-page.css
index bc56fa0..fb1e3a0 100644
--- a/core/themes/seven/maintenance-page.css
+++ b/core/themes/seven/maintenance-page.css
@@ -102,19 +102,19 @@
 /**
  * Layout
  */
-.l-container {
+.layout-container {
   background: #fff;
   width: auto;
   margin-left: 1.25em;
   margin-right: 1.25em;
 }
-.l-container:after { /* no reason for a clearfix in the markup */
+.layout-container:after { /* no reason for a clearfix in the markup */
   content: "";
   display: table;
   clear: both;
 }
 @media all and (max-width: 48em) { /* 768px */
-  .l-container {
+  .layout-container {
     margin: 1.25em;
     padding: 10px 20px;
   }
@@ -138,7 +138,7 @@
     width: 100%;
     height: 100%;
   }
-  .l-container {
+  .layout-container {
     margin: 0 auto;
     max-width: 770px;
     width: 75%;
@@ -165,11 +165,11 @@
     padding: 15px;
     margin: 0.25em 0;
   }
-  .l-sidebar-first {
+  .layout-sidebar-first {
     float: left;
     width: 35%;
   }
-  [dir="rtl"] .l-sidebar-first {
+  [dir="rtl"] .layout-sidebar-first {
     float: right;
   }
 
diff --git a/core/themes/seven/templates/install-page.html.twig b/core/themes/seven/templates/install-page.html.twig
index f86486e..98b3f8a 100644
--- a/core/themes/seven/templates/install-page.html.twig
+++ b/core/themes/seven/templates/install-page.html.twig
@@ -9,7 +9,7 @@
  * @see template_preprocess_install_page()
  */
 #}
-<div class="l-container">
+<div class="layout-container">
 
   <header role="banner">
     {% if site_name or site_slogan %}
@@ -25,9 +25,9 @@
   </header>
 
   {% if page.sidebar_first %}
-    <aside class="l-sidebar-first" role="complementary">
+    <aside class="layout-sidebar-first" role="complementary">
       {{ page.sidebar_first }}
-    </aside>{# /.l-sidebar-first #}
+    </aside>{# /.layout-sidebar-first #}
   {% endif %}
 
   <main role="main">
@@ -39,9 +39,9 @@
   </main>
 
   {% if page.sidebar_second %}
-    <aside class="l-sidebar-second" role="complementary">
+    <aside class="layout-sidebar-second" role="complementary">
       {{ page.sidebar_second }}
-    </aside>{# /.l-sidebar-second #}
+    </aside>{# /.layout-sidebar-second #}
   {% endif %}
 
   {% if page.page_bottom %}
@@ -50,4 +50,4 @@
     </footer>
   {% endif %}
 
-</div>{# /.l-container #}
+</div>{# /.layout-container #}
diff --git a/core/themes/seven/templates/maintenance-page.html.twig b/core/themes/seven/templates/maintenance-page.html.twig
index 9097297..01bc89b 100644
--- a/core/themes/seven/templates/maintenance-page.html.twig
+++ b/core/themes/seven/templates/maintenance-page.html.twig
@@ -9,7 +9,7 @@
  * @see template_preprocess_maintenance_page()
  */
 #}
-<div class="l-container">
+<div class="layout-container">
 
   <header role="banner">
     {% if site_name or site_slogan %}
@@ -25,9 +25,9 @@
   </header>
 
   {% if page.sidebar_first %}
-    <aside class="l-sidebar-first" role="complementary">
+    <aside class="layout-sidebar-first" role="complementary">
       {{ page.sidebar_first }}
-    </aside>{# /.l-sidebar-first #}
+    </aside>{# /.layout-sidebar-first #}
   {% endif %}
 
   <main role="main">
@@ -44,4 +44,4 @@
     </footer>
   {% endif %}
 
-</div>{# /.l-container #}
+</div>{# /.layout-container #}