You can add .ie6 or .ie7 or .ie8 or .ie9 before any CSS you want to target a specific IE browser for, as this special class it's built into Moodle automatically. I think the only reason that IE css file is added into this theme is because it was originally a Moodle 1.9 theme which listed the extra IE css stylesheets in the header.
Fortunately Moodle does not work like that now. So you could in actual fact add .ie to your span.com like so...
.ie span.com { margin-left: 25px; color: #ff0000;}
as the .ie targets ALL ie browsers.
This CSS rule can be added to this theme's Custom CSS settings found at...
Site Administration > Appearance > Themes -> at this point where 'Theme settings', and 'Theme selector' are listed you will also see a list of theme names. These are all the Custom settings pages for individual themes. By clicking on the 'Splash' link you will get the Splash Custon Settings' page. In that page is a CSS text area specifically designed to add CSS so that it overrides other CSS that has already been processed.
It is important to have Theme Designer Mode enabled in Theme settings before your changes to the CSS will be seen.
Hope this helps?
Mary