Add default bottom margin for headings

assets/less/main.less

@@ -1,6 +1,5 @@
 @import (less) "~normalize.css/normalize.css";
 @import (less) "~suitcss-base/lib/base.css";
-
 @import (less) "~font-awesome/css/font-awesome.css";
 @import (less) "~highlightjs/styles/github-gist.css";
 
@@ -34,6 +33,8 @@ img.with-border {
     @apply .border .border-grey-light;
 }
 
+h1, h2, h3 { @apply .mb-2; }
+
 p,
 ul,
 table,