I'm not sure how to go about styling a custom theme Recaptcha widget using

http://github.com/ambethia/recaptcha

I want to resize the widget to fit in a form in a sidebar.

If I do

<%= recaptcha_tags :display => {:theme => 'custom', :custom_theme_widget => 'recaptcha_widget'} %>

and add

<div id="recaptcha_widget">
    <div id="recaptcha_image"></div>
    <input type="text" id="recaptcha_response_field" name="recaptcha_response_field" />
</div>

as per

http://stackoverflow.com/questions/1715575/recaptcha-form-customization

I only get the response input field, and an error message in the source attribute of the img tag

src="http://optim.coral.cs.cmu.edu/error/TypeError_Result_of_expression___recaptcha_response_field__null_is_not_an_object_"

Has anyone found a good way to custom theme the Recaptcha widget using the Ambethia gem?