unify short description styling (#4548)

apply same style class to the About description on both the landing page
and the about/more page

app/javascript/styles/about.scss

@@ -484,7 +484,7 @@
     padding: 0;
   }
 
-  .learn-more-cta {
+  .about-short {
     background: darken($ui-base-color, 4%);
     padding: 50px 0;
   }