Fix pixel values in Responsive Utilities docs to match the actual code

css.html

@@ -1966,8 +1966,8 @@ For example, <code>&lt;section&gt;</code> should be wrapped as inline.
           <tr>
             <th>Class</th>
             <th>Small devices <small>Up to 768px</small></th>
-            <th>Medium devices <small>768px to 979px</small></th>
-            <th>Large devices <small>980px and up</small></th>
+            <th>Medium devices <small>768px to 991px</small></th>
+            <th>Large devices <small>992px and up</small></th>
           </tr>
         </thead>
         <tbody>