diff --git a/aio/src/styles/1-layouts/_content-layout.scss b/aio/src/styles/1-layouts/_content-layout.scss
index 2c03a4b1bef..63dc42416e4 100644
--- a/aio/src/styles/1-layouts/_content-layout.scss
+++ b/aio/src/styles/1-layouts/_content-layout.scss
@@ -4,6 +4,8 @@
 }
 
 .sidenav-content {
+  display: block;  // This is required for browsers that do not recognize `<main>` as a block
+                   // element (such as IE11).
   min-height: 100vh;
   padding: 80px 3rem 2rem;
   max-width: 50em;