Centrer un menu vertical

      <ul>
           <li>Elément 1</li>
           <li>Elément 2</li>
      </ul>

     ul{
           position:fixed;
          padding: 0;
         list-style: none;
        top:50px;
}
      li {
         text-align: center;
       width:120px;
       margin: 3px;
      font-size:20px;
      text-align:center;
      font-weight:bold;
      background-color: yellow;  
}