<form class="navbar-form navbar-left" role="search" action="#" method="get">
  <input type="hidden" value="syui.gitlab.io">
  <div class="form-group">
    <input type="text" class="form-control" placeholder="" name="q">
  </div>
  <button type="submit" class="btn btn-default"><i class="fa fa-search"></i></button>
</form>