Merge branch '25044-md-header-tabs' into 'master'

25044 Make md header tabs match nav tabs

## What does this MR do?
Changes styling of md-header tabs to match navigation tabs

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #25044

See merge request !7801

app/assets/stylesheets/framework/markdown_area.scss

@@ -56,16 +56,9 @@
 
 .md-header {
   .nav-links {
-    .active {
-      a {
-        border-bottom-color: #000;
-      }
-    }
-
     a {
       padding-top: 0;
       line-height: 19px;
-      border-bottom: 1px solid $border-color;
 
       &.btn.btn-xs {
         padding: 2px 5px;