app/views/estimation_items/_form_for_new.html.erb
<%= form_for [@estimation, EstimationItem.new], html: { class: 'form-inline' }, remote: true do |f| %>
<div class="input-group">
<%= f.number_field :value, class: 'form-control value', placeholder: 'Value', autofocus: true %>
</div>
<div class="input-group">
<%= f.text_field :title, class: 'form-control title', placeholder: 'Item title (optional)' %>
<div class="input-group-append">
<%= f.button class: 'btn btn-success', value: 'Add estimation item', type: :submit do %>
<%= icon('plus-circle fa-lg') %>
<% end %>
</div>
</div>
<% end %>