all.scss
css/oldie.scss
css/_utils.scss
css/_global.scss

<!--[if lte IE 8]>
    <link rel="stylesheet" href="path/oldie.css">
<![endif]-->
<!--[if gt IE 8]><!-->
    <link rel="stylesheet" href="path/all.css">
<!--<![endif]-->

@import '_utils';
@import '_global';

$old-ie: true;
$mq-ie: desk;

@import 'all';

// Here we define that by default our users are not using an old browser
// The use of !default allow us to override this variable before this point
$old-ie: false !default;

// Here we define some breakpoints - This can be whatever you want/need
$desk-start: 1000px !default;


// This is where the magic happens
// Our media-query mixin takes one argument, which is the media-query type
@mixin media-query($media-query) {

	// If $old-ie is false, carry on...
    @if $old-ie == false {

    	// Here we check for the argument we passed when we included the media query
    	// If our argument is 'mobile', then go ahead and create our media query
    	// The media query can be anything you want.
        @if $media-query == mobile {
            @media only screen and (max-width: $desk-start) {
            	@content;
            }
        }

        // If our argument is 'desk', then go ahead and create our media query for desktop
        @if $media-query == desk {
            @media only screen and (min-width: $desk-start) {
            	@content;
            }

        }
        
        // If our argument is 'print', we can also set a print media query. win!
        @if $media-query == print {
        	@media print {
        		@content;
        	}
        }
    }

    // Now, if $mq-ie ($mq-ie is defined in oldie.scss) is the same as what we passed
    // Then go ahead and use that block of code.
    // On all.scss we defined $mq-ie as equals to 'desk', so basically what this is doing is
    // Checking for every include of the media-query mixin that uses 'desk' as the argument
    // And using this code as default
    @else if $mq-ie == $media-query {
    	@content;
    }
}

* { margin: 0; padding: 0; }

body {
	background: #737E8C;
	color: #ffffff;
	font-size: 20px;
	line-height: 26px;
	padding: 60px 0 0;

	// This is an example of how to use the media-query mixin
	// Styles in this declaration will only show on desktop
	@include media-query(desk) {
		background: #8C7D73;
	}

}

a {
	color: #333333;
	font-weight: bold;
}

p {
	display: block;
	clear: both;
	padding: 60px 15%;
	text-align: center;
}

.code-sample {
	margin: 3%;

	@include media-query(desk) {
		float: left;
		width: 47%;
		margin: 0 1.5%;
	}
}

pre {
	background: #999999;
	font-size: 16px;
	padding: 0 0 0 20px;
}