mq() is a Sass mixin that helps you compose media queries in an elegant way. It was developed in-house at the Guardian, and is now also in use at BBC Sport and the Financial Times…

• compiles keywords and px/em values to em-based queries (a good thing)
• provides fallbacks for older browsers (see Mobile-first Responsive Web Design and IE8 on the Guardian's developer blog).

1. Install with Bower: bower install sass-mq --save OR Download _mq.scss to your Sass project.
2. Import the partial in your Sass files and override default settings with your own preferences before the file is imported:

   // To enable support for browsers that do not support @media queries,
   // (IE <= 8, Firefox <= 3, Opera <= 9) set $mq-responsive to false
   // Create a separate stylesheet served exclusively to these browsers,
   // meaning @media queries will be rasterized, relying on the cascade itself
   $mq-responsive: true;
   
   // Name your breakpoints in a way that creates a ubiquitous language
   // across team members. It will improve communication between
   // stakeholders, designers, developers, and testers.
   $mq-breakpoints: (
       mobile:  320px,
       tablet:  740px,
       desktop: 980px,
       wide:    1300px,
   
       // Tweakpoints
       desktopAd: 810px,
       mobileLandscape: 480px
   );
   
   // Define the breakpoint from the $mq-breakpoints list that should
   // be used as the target width when outputting a static stylesheet
   // (i.e. when $mq-responsive is set to 'false').
   $mq-static-breakpoint: desktop;
   
   // If you want to display the currently active breakpoint in the top
   // right corner of your site during development, add the breakpoints
   // to this list, ordered by width, e.g. (mobile, tablet, desktop).
   $mq-show-breakpoints: (mobile, mobileLandscape, tablet, desktop, wide);
   
   @import 'path/to/mq';

3. Play around with mq() (see below)

mq() takes up to three optional parameters:

• $from: inclusive min-width boundary
• $until: exclusive max-width boundary
• $and: additional custom directives

Note that $until as a keyword is a hard limit i.e. it's breakpoint - 1.

.responsive {
    // Apply styling to mobile and upwards
    @include mq($from: mobile) {
        color: red;
    }
    // Apply styling up to devices smaller than tablets (exclude tablets)
    @include mq($until: tablet) {
        color: blue;
    }
    // Same thing, in landscape orientation
    @include mq($until: tablet, $and: '(orientation: landscape)') {
        color: hotpink;
    }
    // Apply styling to tablets up to desktop (exclude desktop)
    @include mq(tablet, desktop) {
        color: green;
    }
}

To enable support for browsers that do not support @media queries, (IE <= 8, Firefox <= 3, Opera <= 9) set $mq-responsive: false.

Tip: create a separate stylesheet served exclusively to these browsers, for example with conditional comments.

When @media queries are rasterized, browsers rely on the cascade itself. Learn more about this technique on Jake’s blog.

To avoid rasterizing styles intended for displays larger than what those older browsers typically run on, set $mq-static-breakpoint to match a breakpoint from the $mq-breakpoints list. The default is desktop.

The static output will only include @media queries that start at or span this breakpoint and which have no custom $and directives:

$mq-responsive:        false;
$mq-static-breakpoint: desktop;

.static {
    // Queries that span or start at desktop are compiled:
    @include mq($from: mobile) {
        color: lawngreen;
    }
    @include mq(tablet, wide) {
        color: seagreen;
    }
    @include mq($from: desktop) {
        color: forestgreen;
    }

    // But these queries won’t be compiled:
    @include mq($until: tablet) {
        color: indianred;
    }
    @include mq($until: tablet, $and: '(orientation: landscape)') {
        color: crimson;
    }
    @include mq(mobile, desktop) {
        color: firebrick;
    }
}

@include mq-add-breakpoint(tvscreen, 1920px);

.hide-on-tv {
    @include mq(tvscreen) {
        display: none;
    }
}

While developing, it can be nice to always know which breakpoint is active. To achieve this, set the $mq-show-breakpoints variable to be a list of the breakpoints you want to debug, ordered by width. The name of the active breakpoint and its pixel and em values will then be shown in the top right corner of the viewport.

By default, mq() uses @media all for its queries. If you want to control this (e.g. to output styles for screens only), you can use the $mq-media-type config option to change it (defaults to all):

$mq-media-type: screen;

.screen-only-element {
    @include mq(mobile) {
        width: 300px;
    }
}

@media screen and (max-width: 19.99em) {
    .screen-only-element {
        width: 300px;
    }
}

1. run:

   • Ruby Sass and LibSass:

       ./test.sh
     

   • Ruby Sass

       sass test/test.scss test/test.css --force --sourcemap=none --load-path=./
     

   • Libsass (using node-sass)

       node-sass test/test.scss test/test.css --force --sourcemap=none --include-path=./
     

2. there should be a couple of warnings like this one, this is normal:

    WARNING: Assuming 640 to be in pixels, attempting to convert it into pixels
     on line 74 of _mq.scss, in `mq'
   

3. if git diff test/test.css shows no changes, tests pass

Sass MQ is documented using SassDoc:

npm install -g sassdoc

Then, generate the documentation using:

sassdoc . sassdoc --config .sassdocrc --no-prompt

Generate & deploy the documentation to http://sass-mq.github.io/sass-mq/:

./sassdoc.sh

• https://github.com/alphagov/govuk_frontend_toolkit/blob/master/stylesheets/_conditionals.scss
• https://github.com/bits-sass/helpers-responsive/blob/master/_responsive.scss
• https://gist.github.com/magsout/5978325

• http://jakearchibald.github.io/sass-ie/
• http://nicolasgallagher.com/mobile-first-css-sass-and-ie/
• http://cognition.happycog.com/article/fall-back-to-the-cascade
• http://www.theguardian.com/info/developer-blog/2013/oct/14/mobile-first-responsive-ie8