Synopsis
How to setup and add a .css file to show in the 'Apply CSS Class' drop-down menu in the RadEditor for the product/entity Summary/Description tabs or Topics editing.
Procedure
For ML8:
Once you have created a valid .css file, upload it to your site (ftp to a folder of your choice). Next, edit the file {root}\RadControls\Editor\ConfigFile.xml in a text editor. Scroll to the bottom and add your .css file url between the <item></item> tags in the "CssFiles" property. Save the file back to your site.
Example: <property name="CssFiles">
<item>~/Custom Files/MyStyle.css</item>
</property>
For ML9/MultiStore:
Edit the file where the RAD editor is added to the page (for example, entityEditProduct.aspx) and find the telerik:radeditor invocation, then add a CssFiles node like this:
<CssFiles>
<telerik:EditorCssFile Value="~/App_Themes/Skin_1/test.css" />
</CssFiles>