Thanks. So if I defined a style in my main .css file, say, ".column-style", can I write something like this?

fields: [
          {
            key: 'last_name',
            sortable: true,
            thClass: '.column-style',
          },
          {
            key: 'first_name',
            sortable: false
          },

Probably without the . in the class name.

Thanks. I can update the border now. As for background color, it was overwritten by some existing styles. I guess I can live with using head-variant="light" then. Thanks again.