Rails date_selectをBootstrapを使っていい感じにする ref: http://qiita.com/t_oginogin/items/519fb52e1708e26a8b73

application.css.scss

@import "bootstrap-sprockets";
@import "bootstrap";

.bootstrap-date {
  display: inline-block;
  width: auto;
}

sample.html.erb

  <div class="row">
    <div class="col-xs-3 col-sm-3 col-md-3 col-lg-3">
      stylesheet display設定を追加：
    </div>
    <div class="col-xs-3 col-sm-3 col-md-3 col-lg-3">
      <%= date_select 'date-with-stylesheet-inline', '', {use_month_numbers: true}, {class: "form-control bootstrap-date"} %>
    </div>
  </div>