Cannot get two column layout

So I had my CSS set up a little differently to the main instruction video as I have used it to design my own portfolio. Now I am attempting to make my 1 column contact page change to 2 columns when the media is over 480px, as per the instructional video. However, adding the primary and secondary classes makes no difference at all. Can someone please help? Relevant code as follows:

Contact.html:

<div id="wrapper"> <section class="contact" id="primary"> <h3>General Information</h3> <p>If you are interested in hiring me for a photography assignment or purchasing any of my work, please don't hesitate to contact me!</p> </section> <section class="contact" id="secondary"> <h3>Contact Details</h3> <ul class="contact-info"> <li class="mail"><a href ="mailto:garethfenney@hotmail.com">garethfenney@hotmail.com</a></li> <li class="twitter"><a href ="http://twitter.com/intent/tweet?screen_name=fwsurfer">@FWSurfer</a></li> </ul> </section>

Main.css:

/********************* PAGE: CONTACT **********************/

.contact{

padding: 0 30px; margin: 60px auto 0; text-align: center; width: 80%; max-width: 940px; }

.contact-info { list-style: none; padding: 0; margin: 0 auto; text-align: center; font-size: 0.9em; }

.contact-info a { display: inline-block; min-height: 20px; background-repeat: no-repeat; background-size: 20px 20px; padding: 0 0 0 30px; margin: 0 0 10px; }

.contact-info li.mail a { background-image: url('../img/mail.png'); }

.contact-info li.twitter a { background-image: url('../img/twitter.png'); }

Responsive.css:

@media screen and (min-width 480px) {

/********************* TWO COLUMN LAYOUT **********************/

#primary { width: 50%; float: left; }

#secondary { width: 40%; float: right; }

}