Changing colours on tabs and accordions

Hello,

I have tried changing the colours on the tabs and accordion headings to match my theme but nothing is working. I have tried in the theme css file and the WP Customise Additional CSS with the following:

.nav-pills .nav-link.active, .nav-pills .show >.nav-link {
color: #fff;
background-color: #2d8dc1;
}

I am using a child theme of Understap which uses Bootstrap 5.

Please help, where or how do I style the tabs and accordions?

Cheers,
Tracy