Documentation:
Simple Heading

Here you can control the styling of the module border.

Border Offset

Here you can control the position of the border relative to the module element. Negative values will position the border outside the module element. Positive values will position the border inside the module element.

See here for an example.

Other settings here are common to most Divi modules and are not discussed further. For more information on common Divi module settings, please consult the Elegant Themes Documentation.