diff --git a/index.html b/index.html
index b1296e0..16dc427 100644
--- a/index.html
+++ b/index.html
@@ -93,7 +93,7 @@
     </header>
 
     <main role="main">
-      <article>
+      <article id="webslides" class="vertical">
         <!-- Quick Guide
           - Each parent <section> in the <article id="webslides"> element is an individual slide.
           - Vertical sliding = <article id="webslides" class="vertical">