<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
.example {
width: 350px;
height: 350px;
border: 1px solid #c3c3c3;
display: flex;
flex-direction: column;
}
.example div {
width: 70px;
height: 70px;
}
</style>
</head>
<body>
<h2>Flex-direction property example</h2>
<div class="example">
<div style="background-color: #DC143C;">A</div>
<div style="background-color: #0000CD;">B</div>
<div style="background-color: #9ACD32;">C</div>
<div style="background-color: #666666;">F</div>
</div>
</body>
</html>