The padding for Section Main is not set - all padding fields are blank.
The error is confined to the wiki only since the identified template is specific to VaultWiki (vw_block.css). I've just edited this template by adding an extra hash to the BLOCKS css comment at line 1, and with XenForo's $config['debug'] set to false and then saving this template the error goes away. If I set $config['debug'] to true and save the template again, the error returns.