Use the d-flex class in Bootstrap to create a flexbox container.
Here, I have set two flex items:
<div class="d-flex p-3 bg-primary text-white">
<div class="p-2 bg-success">One</div>
<div class="p-2 bg-danger">Two</div>
</div>
You can try to run the following code to implement the .d-flex class:
Live Demo
<!DOCTYPE html>
<html lang="en">
<head>
<title>Bootstrap Example</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container mt-3">
<h2>Understanding Flex</h2>
<div class="d-flex p-3 bg-primary text-white">
<div class="p-2 bg-success">One</div>
<div class="p-2 bg-danger">Two</div>
</div>
</div>
</body>
</html>