outline buttons

 <button class="btn btn-outline-primary">Primary</button>
 <button class="btn btn-outline-secondary">Secondary</button>
 <button class="btn btn-outline-success">Success</button>
 <button class="btn btn-outline-danger">Danger</button>
 <button class="btn btn-outline-warning">Warning</button>
 <button class="btn btn-outline-info">Info</button>