In order to see images being referenced in a style sheet from Service Studio, you need to also include the Espace name in the File path, such as "/RichWIdgets/green_check.jpg". If you don't include the Espace name, your css link will still run in the browser, but Service Studio doesn't know where to retrieve the preview image from so it won't display anything.
Here are some examples of what we are using:
background: #0154A4 url(/RichWidgets/img/Bar_Gradient.png) repeat-x top; (image stored in RichWidgets Espace) background: #004480 url(/CommonElements/img/Header_Background.jpg) left top no-repeat; (image stored in our Common Espace, same as your HR_Common)
You may also want to check the style hierarchy in either Firefox or IE to make sure a css style isn't being overriden by another style.
I needed to allow access to RichWidgets outside the server. That was why the images, css, etc. .. wasn't recognized. Thanks for your help.
Regards, Vitor Parada