Auto width

Source:  https://www.peeayecreative.com/how-to-set-an-auto-adjusting-divi-menu-dropdown-width/

/* -- START increase dropdown submenu width -- */
@media only screen and (min-width: 981px) {
	.nav li ul {
		width: fit-content;
		display: flex;
		flex-direction: column;
	}
	.nav li li {
		white-space: nowrap;
	}
	.nav li li a {
		width: auto;
	}
}
/* -- END increase dropdown submenu width -- */Code language: CSS (css)

Specified width

If a page title has long words, they break with the standard width. To change this for the standard theme customizer menu:

/* -- START increase dropdown submenu width -- */
.nav li > ul,#top-menu li li {
width: 300px !important;
}
#top-menu li li a {
width: 250px !important;
font-size: 10px;
}
/* -- END increase dropdown submenu width -- */Code language: CSS (css)