arma-server-web-admin/public/js/tpl/missions/workshop.html

<form class="form" role="form" enctype="multipart/form-data">
  <div class="form-group">
    <label for="workshop" class="control-label">Steam Workshop ID</label>
    <input type="number" class="form-control workshop" name="workshop" id="workshop" data-field="workshop">
    <span class="help-block">
      ID can be found in the URL of Workshop i.e.
      <i>https://steamcommunity.com/workshop/filedetails/?id=$id</i>
    </span>
  </div>
  <button type="submit" class="btn btn-primary">Download</button>
</form>