Styling the sidebar widgets

Hi,

I see on the Podcast Plus demo some of the sidebar widgets are styled (eg. the Mailchimp signup box has a grey background) and I want to ask if that styling is related to that widget or the theme itself?

I am currently using the free theme but want to style my Mailchimp widget just like this. Do I need Plus for this or is there a simple CSS style that can be applied on the widget?

Thanks