Add a grey background color to the Bootstrap 4 card

To add a gray background color to the Bootstrap 4 card, use the card class with the bg-dark contextual class −

<div class="card bg-dark text-white">

Set the card body inside the same <div> class −

<div class="card bg-dark text-white">
  <div class="card-body">Hello</div>
</div>

Let us see the complete example add a grey background color to Bootstrap card −

Example

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">
      <h2>Welcome</h2>
      <div class="card bg-dark text-white">
        <div class="card-body">Hello</div>
      </div>
    </div>
</body>
</html>