chore(ng-bootstrap): changing a selector

Author: Konstantin Dinev

src/app/theming/bootstrap/bootstrap-sample.component.scss

@@ -92,7 +92,7 @@ $dark-secondary: color($custom-dark-palette, "secondary");
         ::ng-deep {
             @include bootstrap-dark-theme($custom-dark-palette);
 
-            .accordion {
+            ngb-accordion {
                 .accordion-header {
                     background-color: color($custom-dark-palette, 'grays', 200);
                     color: color($custom-dark-palette, 'grays', 900);