在可滚动的垂直菜单中，子菜单不显示在右侧

Question

添加position:fixed和overflow:scroll属性菜单后滚动但子菜单未显示在右侧栏上或当我删除属性overflow时，右侧栏菜单显示但父菜单不显示滚动。

  <nav id="cssmenu" style="display:none">
    <ul class="level0_category">
    <li class="parentMenus"><a href="#"> Men's Corner </a></li>
    <li class="parentMenus"><a href="#">   Women's Corner </a></li>
    <li class="parentMenus"><a href="#">  House of Electronics </a>
    <ul class="level1_category">
    <li><a href="#">Laptop</a></li>
    <li><a href="#">Mobile</a></li>
    <li><a href="#">Printers</a></li>
    <li><a href="#">AC</a></li>
    <li><a href="#">Refrigerator</a></li>
    </ul>
    </li>
    </ul>
    </nav>

 nav#cssmenu{margin:0 auto;position: fixed; height: 100%; width: 350px;left: -600px}
   

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