add role form for horizontal form example

css.html

@@ -1617,7 +1617,7 @@ For example, <code>&lt;section&gt;</code> should be wrapped as inline.
     <h2 id="forms-horizontal">Horizontal form</h2>
     <p>Use Bootstrap's predefined grid classes to align labels and groups of form controls in a horizontal layout by adding <code>.form-horizontal</code> to the form. Doing so changes <code>.form-group</code>s to behave as grid rows, so no need for <code>.row</code>.</p>
     <div class="bs-example">
-      <form class="form-horizontal">
+      <form class="form-horizontal" role="form">
         <div class="form-group">
           <label for="inputEmail3" class="col-sm-2 control-label">Email</label>
           <div class="col-sm-10">