Adding a :checked pseudo class to an embedded mailchimp form

First of all I'm not really a web developer, so bear with me.

I'm trying to embed a mailchimp signup form on my site. I have a set check-boxes that I'd like to keep hidden unless a certain radio button is selected.

    <!-- Begin MailChimp Signup Form -->
<link href="//cdn-images.mailchimp.com/embedcode/classic-10_7.css" rel="stylesheet" type="text/css">
<style type="text/css">

.reveal{
    display: none !important;
}

#radio-2:checked ~ .reveal {
    display: inline;
}

</style>
<div id="mc_embed_signup">
<form action="n/a" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" novalidate>
    <div id="mc_embed_signup_scroll">

<div class="mc-field-group input-group">
    <strong>Radio Buttons</strong>
    <ul>

<li><input type="radio" id="radio-1" value="Radio 1" name="MMERGE6" id="mce-MMERGE6-0"><label for="mce-MMERGE6-0">Radio 1</label></li>

<li><input type="radio"  id="radio-2" value="Part Time" name="MMERGE6" id="mce-MMERGE6-1"><label for="mce-MMERGE6-1">Part Time</label></li>

</ul>
</div>
<div class="mc-field-group input-group reveal">
    <ul>

<li><input type="checkbox" value="1" name="group[18657][1]" id="mce-group[18657]-18657-0"><label for="mce-group[18657]-18657-0">1</label></li>

<li><input type="checkbox" value="2" name="group[18657][2]" id="mce-group[18657]-18657-1"><label for="mce-group[18657]-18657-1">2</label></li>

<li><input type="checkbox" value="4" name="group[18657][4]" id="mce-group[18657]-18657-2"><label for="mce-group[18657]-18657-2">3</label></li>

<li><input type="checkbox" value="8" name="group[18657][8]" id="mce-group[18657]-18657-3"><label for="mce-group[18657]-18657-3">4</label></li>

</ul>

</div>
    <div id="mce-responses" class="clear">
        <div class="response" id="mce-error-response" style="display:none"></div>
        <div class="response" id="mce-success-response" style="display:none"></div>
    </div>    <!-- real people should not fill this in and expect good things - do not remove this or risk form bot signups-->
    <div style="position: absolute; left: -5000px;" aria-hidden="true"><input type="text" name="b_e7f52c90ee3d55370f2c41bac_8ea8200d35" tabindex="-1" value=""></div>
    <div class="clear"><input type="submit" value="Subscribe" name="subscribe" id="mc-embedded-subscribe" class="button"></div>
    </div>
</form>
</div>
<script type='text/javascript' src='//s3.amazonaws.com/downloads.mailchimp.com/js/mc-validate.js'></script><script type='text/javascript'>(function($) {window.fnames = new Array(); window.ftypes = new Array();fnames[0]='EMAIL';ftypes[0]='email';fnames[1]='FNAME';ftypes[1]='text';fnames[2]='LNAME';ftypes[2]='text';fnames[4]='MMERGE4';ftypes[4]='phone';fnames[6]='MMERGE6';ftypes[6]='radio';}(jQuery));var $mcj = jQuery.noConflict(true);</script>
<!--End mc_embed_signup-->

I want the set of checkboxes here to only reveal when the second radio button is selected.

I can get :checked to work when I write my own form, but I can't seem to get it to work within an embedded mailchimp form, and I can't figure out why. Does anyone have any ideas?