Change the way "add content" and "node's" are displayed
page--node--[content-type].tpl.php = node template for a specific content type (no square brackets)

page--node--add--[content-type].tpl.php = node/add template for specific content type.

Copy/paste the code you have in node.tpl.php and clear your server cache. Now you can add custom classes everywhere or even create a custom HTML structure to render your fields. See the node.tpl.php documentation and Drupal 7 template suggestions.

Hope this helps!