Other content
This is a test simple text block to ensure styles are on the page. The code block itself doesn't bring along styles, but having almost any other content block on a page should be enough to get the styles to stick.
You can also put the code right into any "Full HTML" block (like this one). Just click the "Source" button, paste this code in, then click "Source" again to exit Source mode.
This is the button code:
<button data-fundraising-form="PYEVM6DX" type="button" class="btn btn-default">Donate Now</button>