[Plugin: MailChimp List Subscribe Form] Cannot align/space submit button properly in MailChimp WP pl

Hi, I installed the MailChimp List Subscribe form plugin a few months ago and it works fine. You can see it here, http://www.binichic.com.
The problem is that I can’t modify it to align properly and add some space between the submit button and the email input box right above it. I can’t modify their widths either, in case they can sit next to each other in the same line…
This is the part of the code i have in the “sidebar” of the CSS Editor of my blog where I think the problem might lie:

<div id="mc_embed_signup" style="width: 146px;">
<form action="http://binichic.us2.list-manage.com/subscribe/post?u=91705c9c712886b4db5d833d1&id=eb523110d0" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" style="font: normal 100% Arial, sans-serif;font-size: 10px;">
	<fieldset style="-moz-border-radius: 4px;border-radius: 4px;-webkit-border-radius: 4px;border: 1px solid #fff;padding-top: 1.5em;margin: .5em 0;background-color: #fff;color: #000;text-align: left;">
	<legend style="white-space: normal;text-transform: capitalize;font-weight: bold;color: #000;background: #fff;padding: .5em 1em;border: 1px solid #ccc;-moz-border-radius: 4px;border-radius: 4px;-webkit-border-radius: 4px;font-size: 1.2em;"><span>Subscribe to BiniChic</span></legend>
<div class="mc-field-group" style="margin: 1.3em 5%;clear: both;overflow: hidden;">
<label for="mce-EMAIL" style="display: block;margin: .3em 0;line-height: 1em;font-weight: bold;">Email Address </label>
<input type="text" value="" name="EMAIL" class="required email" id="mce-EMAIL" style="margin-right: 1.5em;padding: .2em .3em;width: 90%;float: left;z-index: 999;">
</div>
		<div id="mce-responses" style="float: left;top: -1.4em;padding: 0em .5em 0em .5em;overflow: hidden;width: 90%;margin: 0 5%;clear: both;">
			<div class="response" id="mce-error-response" style="display: none;margin: 1em 0;padding: 1em .5em .5em 0;font-weight: bold;float: left;top: -1.5em;z-index: 1;width: 80%;background: FBE3E4;color: #D12F19;"></div>
			<div class="response" id="mce-success-response" style="display: none;margin: 1em 0;padding: 1em .5em .5em 0;font-weight: bold;float: left;top: -1.5em;z-index: 1;width: 80%;background: #E3FBE4;color: #529214;"></div>
		</div>
		<div><input type="submit" value="Subscribe" name="subscribe" id="mc-embedded-subscribe" class="btn" style="clear: both;width: auto;display: block;margin: 1em 0 1em 5%;"></div>
	</fieldset>
	<a href="#" id="mc_embed_close" class="mc_embed_close" style="display: none;">Close</a>
</form>
</div>

Thank you in advance for helping me out. I’m new at this css technical stuff and I’m afraid I might have some code that is blocking my ability to modify something.
Also, how hard or easy is it to change the look of the submit button?

http://ww.wp.xz.cn/extend/plugins/mailchimp/