Add version badge to documentation header

docs/_docs/variables.md

@@ -34,7 +34,8 @@ The following is a reference of the available data.
   </p>
 </div>
 
-## Theme
+## Theme Variables {%- include docs_version_badge.html version="4.3.0" -%}
+{: #theme-variables }
 
 {% include docs_variables_table.html scope=site.data.jekyll_variables.theme %}