Hey Laurent,
The navbar in the splash page has some customizations to it that is why it has the separators.
To change the background color of the navigation area, please add this code in X > Theme Options > CSS:
.masthead .x-navbar {
background-color: #333;
}
.x-navbar .desktop .x-nav>li:not(:last-child) {
border-right: 1px solid #171717;
box-shadow: inset -1px 0 0 0 rgba(255, 255, 255, 0.065);
}
And to make it fixed on mobile, please add this code as well:
@media (max-width: 979px) {
.x-navbar-fixed-top {
position: relative;
}
}
Kindly note that since this is a custom code that changes the default behavior/display of the theme, you will be responsible to maintain or update the code in case you require further changes or if the code stops working in future updates. If you are uncertain how to proceed, it would be best to get in touch with a developer.
Hope this helps.