Source: http://www.divithemeexamples.com/divithemelayouts/two-cafe-divi-theme-layout/

Add the following custom CSS (main element) to the module on the right. Note: this doesn’t look nice on mobile.

Note: you can also do this with the border setting on the Divi module design tab.

border-left: 1px solid #333;Code language: CSS (css)