AdminLTE/scss/dark/layout/_main-header.scss

.main-header {
  background-color: $dark-alt;
  border-bottom-color: tint-color($dark-alt, 10%);

  .nav-link {
    color: $gray-400-alt;

    &:hover,
    &:focus {
      color: $white-alt;
    }
  }
}