show error message in html

<div class="container" id="main">
      <div class="alert alert-warning alert-dismissible fade show" role="alert">
        <strong>Holy guacamole!</strong> You should check in on some of those fields below.
        <button type="button" class="close" data-dismiss="alert" aria-label="Close">
          <span aria-hidden="true">&times;</span>
        </button>
      </div>
</div>