Bootstrap Well
The Bootstrap well component provides a quick way to apply a simple inset effect to an element.  The class .well is used with <div> element to add well.
<!DOCTYPE html>
<html>
<head>
   <title>Bootstrap Well</title>
   <meta name="viewport" content="width=device-width,initial-scale=1">
   <link rel="stylesheet" type="text/css" href="css/bootstrap.min.css">
   <script type="text/javascript" src="js/jquery.min.js"></script>
   <script type="text/javascript" src="js/bootstrap.min.js"></script>
</head>
<body>
 
<div class="container"> 
  <div class="well">Hi! I am a Well.</div>  
</div>  
 
</body>
</html>
Output :
Hi! I am a Well.
Bootstrap Well Size
The bootstrap size of the well by adding the .well-sm class for small wells or .well-lg class for large wells
<!DOCTYPE html>
<html>
<head>
   <title>Bootstrap Well Size</title>
   <meta name="viewport" content="width=device-width,initial-scale=1">
   <link rel="stylesheet" type="text/css" href="css/bootstrap.min.css">
   <script type="text/javascript" src="js/jquery.min.js"></script>
   <script type="text/javascript" src="js/bootstrap.min.js"></script>
</head>
<body>
 
<div class="container"> 
 
  <div class="well well-sm">This is Small Well</div>  
  <div class="well">This is Medium Well (By Default)</div>  
  <div class="well well-lg">This is Large Well</div>  
  
</div>  
 
</body>
</html>
Output :
This is Small Well
This is Medium Well (By Default)
This is Large Well