diff --git a/theme/classic/templates/contentonly.mustache b/theme/classic/templates/contentonly.mustache
index cb5d9c200f8..2e4e1f7bb38 100644
--- a/theme/classic/templates/contentonly.mustache
+++ b/theme/classic/templates/contentonly.mustache
@@ -53,7 +53,7 @@
 
     <div id="page" class="container-fluid">
         <div id="page-content" class="row">
-            <div id="region-main-box" class="col-xs-12">
+            <div id="region-main-box" class="col-12">
                 <section id="region-main" aria-label="{{#str}}content{{/str}}">
                     {{{ output.course_content_header }}}
                     {{{ output.main_content }}}