<a title="Текст подсказки." class="title_style">Ссылка на полезный ресурс</a>

<style type="text/css">
    
  .title_style{
      display: inline;
      position: relative;
  }
  
  .title_style:hover:after{
      background: #333;
      background: rgba(0,0,0,.8);
      border-radius: 5px;
      bottom: 26px;
      color: #fff;
      content: attr(title);
      left: 20%;
      padding: 5px 15px;
      position: absolute;
      z-index: 98;
      width: 220px;
  }
  
  .title_style:hover:before{
      border: solid;
      border-color: #333 transparent;
      border-width: 6px 6px 0 6px;
      bottom: 20px;
      content: "";
      left: 50%;
      position: absolute;
      z-index: 99;
  }
    
    </style>