Recaptcha creates iFrame on page, breaks styling

Try the CSS below:

/* ReCaptcha Iframe FIX */
iframe {display:none !important;}
header iframe,
section iframe,
footer iframe,
div iframe { display:inline; }

If you don’t have any other frames on the site to worry about, a simpler version should suffice:

iframe {display:none !important;}

Alternatively, you could target all iframes where src="https://stackoverflow.com/questions/8155645/about:blank":

iframe[src="https://stackoverflow.com/questions/8155645/about:blank"]{display:none;}