it seems like he set his layout to only have two columns
then he gave the text element on the right a class of "black_bg" (right click text element, set html class and id)
then he went to lay options → custom css & html
and used this css:
.black_bg {
background-color: #232323;
}
you could also just set a right background image and use a small black image xD
Screenshot 2023-10-07 at 10.37.39.png