W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
}

/* The grid: Three equal columns that floats next to each other */
.column {
  float: left;
  width: 33.33%;
  padding: 50px;
  text-align: center;
  font-size: 25px;
  cursor: pointer;
  color: white;
}

.containerTab {
  padding: 20px;
  color: white;
}

/* Clear floats after the columns */
.row:after {
  content: "";
  display: table;
  clear: both;
}

/* Closable button inside the container tab */
.closebtn {
  float: right;
  color: white;
  font-size: 35px;
  cursor: pointer;
}
</style>
</head>
<body>

<div style="text-align:center">
  <h2>Expanding Grid</h2>
  <p>Click on the boxes below:</p>
</div>

<div class="row">
  <div class="column" onclick="openTab('b1');" style="background:green;">
    Box 1
  </div>
  <div class="column" onclick="openTab('b2');" style="background:blue;">
    Box 2
  </div>
  <div class="column" onclick="openTab('b3');" style="background:red;">
    Box 3
  </div>
</div>

<div id="b1" class="containerTab" style="display:none;background:green">
  <span onclick="this.parentElement.style.display='none'" class="closebtn">&times;</span>
  <h2>Box 1</h2>
  <p>Lorem ipsum dolor sit amet, te quo doctus abhorreant, et pri deleniti intellegat, te sanctus inermis ullamcorper nam. Ius error diceret deseruisse ad</p>
</div>

<div id="b2" class="containerTab" style="display:none;background:blue">
  <span onclick="this.parentElement.style.display='none'" class="closebtn">&times;</span>
  <h2>Box 2</h2>
  <p>Lorem ipsum dolor sit amet, te quo doctus abhorreant, et pri deleniti intellegat, te sanctus inermis ullamcorper nam. Ius error diceret deseruisse ad</p>
</div>

<div id="b3" class="containerTab" style="display:none;background:red">
  <span onclick="this.parentElement.style.display='none'" class="closebtn">&times;</span>
  <h2>Box 3</h2>
  <p>Lorem ipsum dolor sit amet, te quo doctus abhorreant, et pri deleniti intellegat, te sanctus inermis ullamcorper nam. Ius error diceret deseruisse ad</p>
</div>

</body>
</html>

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<!DOCTYPE html><html><head><meta name="viewport" content="width=device-width, initial-scale=1"><style>* {  box-sizing: border-box;}​body {  margin: 0;  font-family: Arial, Helvetica, sans-serif;}​/* The grid: Three equal columns that floats next to each other */.column {  float: left;  width: 33.33%;  padding: 50px;  text-align: center;  font-size: 25px;  cursor: pointer;  color: white;}​.containerTab {  padding: 20px;  color: white;}​/* Clear floats after the columns */.row:after {  content: "";  display: table;  clear: both;}​/* Closable button inside the container tab */.closebtn {  float: right;  color: white;  font-size: 35px;  cursor: pointer;}</style></head><body>