botão máximo de bootstrap de largura
<button type="button" class="btn btn-primary btn-block">Button Name</button>
Snippets
<button type="button" class="btn btn-primary btn-block">Button Name</button><button type="button" class="btn btn-primary btn-sm">Small button</button>
<button type="button" class="btn btn-secondary btn-md">Medium button</button>
<button type="button" class="btn btn-secondary btn-lg">Large button</button>Create block level buttons—those that span the full width of a parent—by adding .btn-block.