Hello,
I just took a look at the website and by using chrome dev tools, it looks like the 'x' you are referring to is there, only its margin bottom is pushing it out of the page. I'm a web dev/designer I make both wordpress and pure code website, to show you that I'm familiar with mailchimp, here is a link for my latest project that has 3 mailchimp forms. Feel free to contact me if you have any questions.
Thanks