fix: padding for empty title callouts (#308)

assets/styles/_callouts.scss

@@ -114,6 +114,10 @@ blockquote[class*="-callout"] > p:first-child {
   }
 }
 
+blockquote[class*="-callout"] > p:empty {
+  padding: 1.2em 35px;
+}
+
 $summary: summary, abstract, tldr;
 $bug: bug;
 $danger: danger, error;