Make CSS classes styled in WYSIWYG How can I make CSS classes that can be added to content in a WYSIWYG style in the edit view?

I've added the following 'CSS classes' and I've used my site's normal CSS to float them left and right respectively and give them a width of 51%:

Left=div.posLeft
Right=div.posRight


When I save the node this works fine. However in the editor the styles are not shown. How can I make them show up?
As @tenken says, on the WYSIWYG profile edit page, under the 'CSS' panel, in the 'CSS path' filed you can link to a CSS file to be used on the edit view. 

/admin/config/content/wysiwyg/profile/PROFILE-NAME/edit