TOOLTIP
Run 
<!DOCTYPE html>
<html>
<head>
  <title>CSS Tooltip</title>
  <style>
    .tooltip {
      position: relative;
      display: inline-block;
      border-bottom: 1px dotted black;
      font-size: 30px;
    }

    .tooltip .tooltiptext {
      visibility: hidden;
      width: 120px;
      background-color: black;
      color: #fff;
      text-align: center;
      border-radius: 6px;
      padding: 5px 0;
      position: absolute;
      z-index: 1;
      top: -5px;
      right: 110%;
      margin-left: -60px;
      opacity: 0;
      transition: opacity 1s;
    }

    .tooltip:hover .tooltiptext {
      visibility: visible;
      opacity: 1;
    }
  </style>
</head>
<body style="text-align:center;">
  <div class="tooltip">Hover over me
    <span class="tooltiptext">Tooltip text</span>
  </div>
</body>
</html>