btn block in bootstrap code example

Example 1: bootstrap Buttons

Bootstrap includes several predefined button styles, each serving its own
semantic purpose, with a few extras thrown in for more control.
Using color to add meaning only provides a visual indication, which will
not be conveyed to users of assistive technologies – such as screen readers. 
Ensure that information denoted by the color is either obvious from the 
content itself (e.g. the visible text), or is included through alternative
means, such as additional text hidden with the .sr-only class.

<button type="button" class="btn btn-primary">Primary</button>
<button type="button" class="btn btn-secondary">Secondary</button>
<button type="button" class="btn btn-success">Success</button>
<button type="button" class="btn btn-danger">Danger</button>
<button type="button" class="btn btn-warning">Warning</button>
<button type="button" class="btn btn-info">Info</button>
<button type="button" class="btn btn-light">Light</button>
<button type="button" class="btn btn-dark">Dark</button>

<button type="button" class="btn btn-link">Link</button>

Example 2: bootstrap Button tags

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

When using button classes on <a> 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.

<a class="btn btn-primary" href="#" role="button">Link</a>
<button class="btn btn-primary" type="submit">Button</button>
<input class="btn btn-primary" type="button" value="Input">
<input class="btn btn-primary" type="submit" value="Submit">
<input class="btn btn-primary" type="reset" value="Reset">