Increase the width of the submenu in just one submenu column and Megamenu

I’m using Beaver Themer, Beaver Builder Child Theme, and the Advanced Menu module from PowerPack Beaver Addons. On the website I’m redesigning, there are 6 menu items. One of the menu items called “Programs” has 17 items in the submenu (they offer a lot of programs!). Is there a way of increasing the width of only this one submenu column rather than all of the submenus? I’d like to make sure these submenu items do not wrap so that the submenu column is not so long. In this forum, someone had posted the following code which I put in the BB Child theme editor but it didn’t do anything (unless I’m not putting the CSS in the right place).
.fl-page-header .fl-page-nav-wrap .navbar-nav ul.sub-menu {
width: auto;
white-space: nowrap;
Any other suggestions for dealing with this large number of submenu items is welcomed. I tried using the megamenu and making 3 columns (by putting in “dummy” Mega Headings and setting it to “hide-heading”, then nesting 5-6 real menu items underneath each mega heading). While the columns were made, it was not pretty. The 3 columns were spaced way too far apart and, again, the width of the submenu item was not wide enough to allow for the text to flow on only one line. Thanks!