Update border-radius docs design

Author: mrmrs

src/templates/docs/border-radius/index.html

@@ -75,7 +75,7 @@ <h1 class="f4 ttu tracked fw6">Reference</h1>
     <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/border-radius" class="link fw6 blue dim">MDN - Border Radius</a>
   </div>
 </div>
-      <section class="bg-dark-gray white pt4 pb5">
+      <section class="bg-near-white black-70 pt4 pb5">
 <header class="ph3 ph5-ns pt4">
         <kbd class="yellow">src/_border-radius.css</kbd>
 </header>