disabled class in bootstrap 4 code example

Example 1: bootstrap 4 button size

Large button
Small button

Example 2: bootstrap Button tags

The .btn classes are designed to be used with the  element. 
However, you can also use these classes on  or  elements
(though some browsers may apply a slightly different rendering).

When using button classes on  elements that are used to trigger in-page 
functionality (like collapsing content), rather than linking to new pages or 
sections within the current page, these links should be given a role="button" 
to appropriately convey their purpose to assistive technologies such as screen 
readers.

Link
Button