Bootstrap

Center a heading

<h2 class="text-center">your text</h2>

Button

Normally, your button elements with the btn and btn-default classes are only as wide as the text that they contain. For example:

<button class="btn btn-default">Submit</button>

This button would only be as wide as the word "Submit".

Submit

By making them block elements with the additional class of btn-block, your button will stretch to fill your page's entire horizontal space and any elements following it will flow onto a "new line" below the block.

<button class="btn btn-default btn-block">Submit</button>

This button would take up 100% of the available width.