Examples: make use of core utils in more places.

site/content/docs/4.3/examples/starter-template/index.html

@@ -40,7 +40,7 @@ extra_css:
 
 <main role="main" class="container">
 
-  <div class="starter-template">
+  <div class="starter-template text-center py-5 px-3">
     <h1>Bootstrap starter template</h1>
     <p class="lead">Use this document as a way to quickly start any new project.<br> All you get is this text and a mostly barebones HTML document.</p>
   </div>

site/content/docs/4.3/examples/starter-template/starter-template.css

@@ -1,7 +1,3 @@
 body {
   padding-top: 5rem;
 }
-.starter-template {
-  padding: 3rem 1.5rem;
-  text-align: center;
-}