noyer71 Hi
I think you could try to use Inspect Element in browser you're using, right click on any element, you will see how it's styled and customize as you wish.
Something like this:
.t4-megamenu .dropdown-menu li > a, .t4-megamenu .dropdown-menu li > .nav-link, .t4-megamenu .dropdown-menu li .dropdown-item {
color: #ffffff !important;
}
.t4-megamenu .dropdown > .dropdown-menu {
background: #7d7777;
}
and put into the custom.css file of template.