[ticket/11150] Adds an overflow to composer output

PHPBB3-11150

phpBB/adm/style/detailled_message_body.html

@@ -5,11 +5,13 @@
 	<p>{{ MESSAGE_TEXT }}</p>
 </div>
 
+<div style="overflow-x:scroll">
 	<fieldset>
 		{%- if MESSAGE_DETAIL_LEGEND -%}
 			<legend>{{ MESSAGE_DETAIL_LEGEND|nl2br }}</legend>
 		{%- endif -%}
 		<pre>{{ MESSAGE_DETAIL }}</pre>
 	</fieldset>
+</div>
 
 <!-- INCLUDE overall_footer.html -->