What is the proper way to dynamically add a button to footer?

Assuming I have 2 buttons:

<div data-role=”button” data-inline=”false” data-style=”round”>Ok</div>
<div data-role=”button” data-inline=”false” data-style=”round”>Cancel</div>

which are rendered and styled as 2 buttons in footer with the same width (180px in my case or half of the footer).

I want to add new button dynamically by some action

<div data-role=”button” data-inline=”false” data-style=”round”>Undo</div>

So that all 3 buttons will be with the same size, have the same style, etc.