New 4.0 secondary-navigation re-uses .nav-tabs class uneccesarily

Bootstrap has .navs that then can be specialized with .nav-tab, .nav-pill or styled differently by leaving those off.

The new sub-menu navigation uses .nav-tab, but then removes all the nav-tab styling and replaces it. If someone tried to style the actual .nav-tabs (the ones that look like paper folder 'tabs') for use elsewhere then the styles would bleed over into these navs.

Just removing the nav-tab should work fine and pick up the base nav styles:

https://getbootstrap.com/docs/4.0/components/navs/#base-nav

The moremenu CSS already adds the hover states and active underline.

And the secondary-navigation would no longer need to override them:

 .secondary-navigation {

    max-width: $course-content-maxwidth;

    margin: 0 auto;

    padding-bottom: 15px;

    .navigation {

        border-top: 1px solid $nav-tabs-border-color;

        border-bottom: 1px solid $nav-tabs-border-color;

        height: calc(#{$moremenu-height} + 2px);

        background-color: $body-bg; 

        .nav-tabs {

            border: none;

            .nav-link {

                border-radius: initial;

            }

        }

About half of that is just remove the styles added by nav-tab.

I'd also recommend using a seperate variable for the border-top/bottom color, rather than re-use the tab one since these are navs, but not tabs in the standard theme.