<%= form_tag admin_topic_search_path, method: :get, remote: params[:controller] == 'topics', class: 'admin-search submit-loader form-inline form-horizontal', id: 'search-form' do %>
  <div class="form-group">
    <div class="col-xs-12 col-sm-7 col-md-7">
      <%= text_field_tag('q', nil, placeholder: t(:search, default: 'Search'), value: params[:q], class: 'form-control search-field', style: "width: 100%;" )%>
    </div>
    <div class="col-sm-2 col-md-2 hidden-xs text-center">
      <div class="input-group date">
        <%= text_field_tag :start_date, nil, class: 'form-control' %>
        <span class="input-group-addon"><i class="glyphicon glyphicon-th"></i></span>
      </div>
    </div>
    <div class="col-sm-2 col-md-2 hidden-xs text-center">
      <div class="input-group date">
        <%= text_field_tag :end_date, nil, class: 'form-control' %>
        <span class="input-group-addon"><i class="glyphicon glyphicon-th"></i></span>
      </div>
    </div>
    <div class="submit-group col-sm-1 col-md-1 text-right">
      <%= submit_tag t('search', default: 'Search'), class: 'btn btn-default' %>
    </div>
  </div>
<% end %>

<%= form_tag admin_topic_search_path, method: :get, remote: params[:controller] == 'topics', class: 'admin-search submit-loader form-inline form-horizontal', id: 'search-form' do %>
  <div class="form-group">
    <div class="col-xs-8 col-sm-7 col-md-7">
      <%= text_field_tag('q', nil, placeholder: t(:search, default: 'Search'), value: params[:q], class: 'form-control search-field', style: "width: 100%;" )%>
    </div>
    <div class="col-sm-2 col-md-2 hidden-xs text-center">
      <div class="input-group date">
        <%= text_field_tag :start_date, nil, class: 'form-control' %>
        <span class="input-group-addon"><i class="glyphicon glyphicon-th"></i></span>
      </div>
    </div>
    <div class="col-sm-2 col-md-2 hidden-xs text-center">
      <div class="input-group date">
        <%= text_field_tag :end_date, nil, class: 'form-control' %>
        <span class="input-group-addon"><i class="glyphicon glyphicon-th"></i></span>
      </div>
    </div>
    <div class="submit-group col-xs-4 col-sm-1 col-md-1 pull-right">
      <%= submit_tag t('search', default: 'Search'), class: 'btn btn-default' %>
    </div>
  </div>
<% end %>

Fix breakpoints on search form
Fix breakpoints on search form
