Docs: display examples based on the docs current color mode (#37562)

* Docs: display examples based on the docs current color mode

* Fix _default/examples.html

site/content/docs/5.3/examples/checkout/index.html

@@ -5,7 +5,7 @@ extra_css:
   - "checkout.css"
 extra_js:
   - src: "checkout.js"
-body_class: "bg-light"
+body_class: "bg-body-tertiary"
 ---
 
 <div class="container">
@@ -44,7 +44,7 @@ body_class: "bg-light"
             </div>
             <span class="text-muted">$5</span>
           </li>
-          <li class="list-group-item d-flex justify-content-between bg-light">
+          <li class="list-group-item d-flex justify-content-between bg-body-tertiary">
             <div class="text-success">
               <h6 class="my-0">Promo code</h6>
               <small>EXAMPLECODE</small>