In Bootstrap 3 Panels which are now cards in bootstrap 4 you were able to add a style such primary, warning, danger, etc. Can this be done with cards? I can’t seem to find a way to do it or any documentation on doing it on the bootstrap site.
<div class="card bg-primary">
<div class="card-body">Basic card</div>
</div>
Just change bg-primary to warning or info etc. https://www.w3schools.com/bootstrap4/bootstrap_cards.asp
That changes the entire card though. I only need to change header and borders. At least the header.
<div class="card">
<div class="card-header bg-primary">Header</div>
<div class="card-body">Content</div>
<div class="card-footer bg-danger">Footer</div>
</div>
Thanks @psweb, it’s not quite ideal like the old panels but it will have to do. All the best in the new year! 
Just out of interest if you want more control you can also use things like text-success border-success bg-warning. As well as add padding and margins so I am generally able to get what I want by using a combination of those.
I even use nav stuff in a card in one of my stranger projects and that worked surprisingly well.
If there is something particular you are trying to achieve just give an idea and I will try assist where possible.
Thanks again, Paul! That extra bit of info helped a lot to achieve the look I needed.