Tables style should not rely on scope attribute

[deniak]

Describe the issue
The table component relies on the scope attribute to style the headers.

th[scope="col"] {
  background-color: #024488;
  color: #fff;
}

Removing/Forgetting that attribute will remove the blue background.

Recommended solution
Updating the selector to thead > th will make that attribute optional and ensure all the tables have the same style.

Additional request
We might also need the same changes for tables footer tfoot.