Well, to get Bootstrap working, first install [Less Rails Bootstrap][lrb].
Then create a button with a [fancy icon][fi] like so:
<%= link_to raw('<i class="icon-trash icon-white"></i>'), card, confirm: 'Are you sure?', method: :delete, :class => 'btn btn-danger' %>Note that you have to link to raw to get it to not escape the HTML.