How can I remove the border around a CMS block?

The border as well as the background colour and the margin under a CMS block come from ThemeWare® CMS styling.

You can activate or deactivate the CMS styling of ThemeWare® for different page types. In addition, you can customise each CMS block with special CSS classes.

You can find more information on this in the following instructions:

ThemeWare® CMS styling for Shopping Experiences