If you select the whole div block and choose the css class in the drop down, the css class will be applied to the whole div block.

 

If you select some text content inside the div block, the inline style will be applied to the selected content.

 

By default, inline style of cute editor will use span.

 

You can set Editor.UseFontTags Property to use font tags for inline styles.

 

Hope it helps.

Let me know if you have any further questions.