feat(aio): copy code snackbar and design updates

- Add snackbar and pointer cursor for copy code button inside aio-code components
- Flex cenetered content in features page
- Removed duplicate global css class
- Add styles to links inside of sub-sections
- Remove focus outline on top nav bar links

aio/content/marketing/features.html

@@ -1,6 +1,6 @@
 <h1>Features &amp; Benefits</h1>
 <article class="l-content ">
-  <div>
+  <div class="flex-center">
     <div><h2 class="text-headline">Cross Platform</h2>
       <div class="feature-row">