Hello Photopost is coded to a default vbulletin style meaning we will correct or autorewrite vbulletin normal url's etc. We do not autorewrite custom stylesheets. You solution is to do one of two things.
1. In Vbulletin Admin => Styles view the stylesheet and edit the relative paths to images and make them full url's this will correct this issue
2. You can modify our file header-inc.php at your descretion to include the ambience directory in the autorewrite code. You can replace the codeblock below in that file with this. You should be able to find it
Content visible to verified customers only.
We only use the vbulletin css we are not going to pick up any hard coded templates