Make the nav look like tabs by setting the tabs prop.
Use the pill style by setting the pills prop.
To proportionately fill all available space with your
<b-nav-item> components, set the
fill prop. Notice that all horizontal space is
occupied, but not every nav item has the same width.
For equal-width elements, set the justified prop
instead. All horizontal space will be occupied by nav links, but
unlike fill above, every
<b-nav-item> will be the same width.