Adapt CSS to the new form name (main_form)

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@8146 20353a03-c40f-0410-a6d1-a30d3c3de9de

bt5/erp5_xhtml_style/SkinTemplateItem/portal_skins/erp5_xhtml_style/erp5.css.xml

@@ -393,7 +393,7 @@ body {\n
   background-color: <dtml-var background_color>;\n
 }\n
 \n
-#body {\n
+#main_form {\n
   background-color: inherit;\n
   color: inherit;\n
 }\n