Untitled

<head>
 <style>
    .center_down {
  display: block;
  margin-left: 20%;
  margin-right: 10%;
  width: 50%;
  position: relative;
  top: 100px;
  overflow-y: hidden;
}
  </style>
    </head>
<body>
<img class="center_down" name="slide" src="piscina.png" onclick="slideAhead();setInterval(invisible, 300)"/>
</body>