Combine sets of <div class="btn-group"> into a <div class="btn-toolbar"> for more complex components.

<div class="btn-toolbar" role="toolbar" aria-label="...">
  <div class="btn-group" role="group" aria-label="...">...</div>
  <div class="btn-group" role="group" aria-label="...">...</div>
  <div class="btn-group" role="group" aria-label="...">...</div>
</div>