Advanced users can use SharePoint Designer to customize the site skin by modifying *.CSS and *.XSLT files.
All files in the Skin folder can be modified, but we recommend that only users with knowledge of CSS/XSLT design make changes to these files.
Make sure to do a backup before making any changes.
In addition, we recommend that you do not modify any of the following files:
Do not modify ANY .aspx file in the Admin folder.