It sounds like you've made changes to the attached_files.css template before. Work out what these changes were, put them into EXTRA.css and then revert the template.
EXTRA.css is a spare .css template which will never be overwritten by an upgrade. You can put any CSS changes in there that you like and they'll always be applied. You may only very occasionally find that some changes in EXTRA.css don't apply. In cases like this, add !important to the end of your property.
The !important will be sure to override the default behaviour.