@import includes another stylesheet within the current one and adds extra rules from the external stylesheet to those already defined. It's a good way of splitting up the styles into different sections if you have a large CSS file, though I must admit I'm not sure why it's been used in your theme.
HTML Code:
@import url('/css/typography.css');
@import url('/css/layout.css');
@import url('/css/color.css');
Good writeup here.
The stylesheet you want to edit is here
Code:
http://digitalartempire.com/wp-content/themes/titan/stylesheets/master.css