Adding a CSS class around Custom Field Group

Hello,
I need to add a custom class around the collapsible "extra field group" in the property details page. This is the page that has all of the information about the property. Which file and line do I need to edit to wrap the span around the custom fields?

Hi Jason,
I can't tell you extractly lines that you can modify the css and code of that part, because there are a lot lines and if you don't know about php and Joomla coding + css style, you can't simple to modify it.
The collapsible "extra field group" elements are in file
components > com_osproperty > template > default > details.html.tpl.php
and
components > com_osproperty > template > default > small.details.html.tpl.php
Please remember that when you modify the css of the collapsible "extra field group" it will effect to all other collapsible information group in details page.
I suggest you to use tool : Inspector element of firefox to debug the css of those span tag.
Good luck
Dam