Simple menu on desktop / Accordion on mobile

[yuri-andrei]

Hi everyone,
It seems that achieving this simple structure has become quite complex. The goal is simple: a have a menu with a title and three sub-itens and I want it to be shown as an accordion on mobile BUT as a simple list menu on desktop (meaning NO dropdown or Drilldown, just a simple list menu). Im using this line of code:

<ul class="vertical medium-vertical menu" data-responsive-menu="accordion medium-menu">
    <li>

      <a href="">Menu 1</a>
      <ul class="vertical menu">
        <li><a href="#">sub-item 1</a></li>
        <li><a href="#">sub-item 2</a></li>
        <li><a href="#">sub-item 3</a></li>
      </ul>

    </li>
  </ul>

No matter how a change these classes, I get the same result: either accordion on both viewports, or simple list menu again on both viewports.

What Im doing wrong here?!
Thanks!