A well is a container in <div> that causes the content to appear sunken or an inset effect on the page. To create a well, simply wrap the content that you would like to appear in the well with a <div> containing the class of .well. The following example shows a default well −
<div class = "well">Hi, am in well !!</div>
You can change the size of well using the optional classes such as, well-lg or well-lg. These classes are used in conjunction with .well class. These affect the padding, making the well larger or smaller depending on the class.
<div class = "well well-lg">Hi, am in large well !!</div> <div class = "well well-sm">Hi, am in small well !!</div>