Display a flex container as Flexible by using display property and change the flex items size to 50px
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Static Template</title>
<style>
.flex-container {
display: flex;
background-color: dodgerblue;
}
.flex-container >div {
margin: 10px;
padding: 20px;
width: 50px;
height: 50px;
font-size:50px;
text-align: center;
background-color: #f1f1f1;
}
</style>
</head>
<body>
<div class="flex-container">
<div>1</div>
<div>2</div>
<div>3</div>
</div>
</body>
</html>