You can apply CSS to the selected text inside the editor by selecting a CSS class name from the Apply CSS
dropdown, which is a customized toolbar dropdownlist item created as follows:

1. Add the following to your editor XML file:

<ToolbarItem Type="DropDown" ID="ApplyCSS" Command="None" />

2. Add items to your Apply CSS dropdown inside ToolbarItemRender event handler in the page code file.

3. Add ApplyCSS client-side JavaScript method to apply the CSS class to the selected text inside the editor.