Use .blockquote class in V4 examples page

Created by: kkirsche

Fix #17888 (closed)

docs/content/reboot.md

@@ -272,7 +272,7 @@ The `<address>` element is updated to reset the browser default `font-style` fro
 The default `margin` on blockquotes is `1em 40px`, so we reset that to `0 0 1rem` for something more consistent with other elements.
 
 <div class="bd-example">
-  <blockquote>
+  <blockquote class="blockquote">
     <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante.</p>
     <footer>Someone famous in <cite title="Source Title">Source Title</cite></footer>
   </blockquote>