CSS in responsive design

What’s in this topic

Stylesheets are the main tool in responsive web design (RWD) implementation. This topic describes the mechanisms and approaches to building RWD used in the default Magento themes. To re-use them in your custom theme, make your theme inherit from the Magento Blank theme.

Mobile first

In the Blank and Luma themes, the mobile first approach is used. It means that the styles for mobile devices (screen width less than 768px) are extended by the styles for the higher breakpoints. As the result, the extra styles are never loaded when a store is viewed on a mobile device.

The mobile and desktop styles are defined in separate files:

  • styles-l.less is used to generate desktop-specific styles (768px and higher).
  • styles-m.less is used to generate basic and mobile-specific styles.

Breakpoints

Breakpoints are used in the CSS code to set up the screen width at which the design switches from the mobile to the desktop version.

The Blank and Luma themes use LESS variables to implement the following breakpoints:

  • @screen__xxs: 320px
  • @screen__xs: 480px
  • @screen__s: 640px
  • @screen__m: 768px (in the Blank and Luma themes, this breakpoint switches between mobile and desktop views)
  • @screen__l: 1024px
  • @screen__xl: 1440px

You can change these breakpoints and add new ones in your custom theme. For instructions see the Add a new breakpoint topic.

Media queries in Magento default themes

The Blank and Luma theme styles are based on the Magento UI library. The library uses CSS3 media queries, an extension of the @media rule, to adapt the layout to the screen width.

The approach implemented in the Magento UI library, uses @media-common style group separation and .media-width() mixins which can be used in any .less file in a theme, as many times as needed, but it is invoked only once, in lib/web/css/source/lib/_responsive.less. The resulting styles-m.css and styles-l.css both have only one call of each media query with all the rules there, instead of multiple calls for the same query.

If working on a theme which inherits from either the Blank or Luma theme, it’s recommended to use .media-width() and style groups separation. Otherwise the style rules will be added twice, once to styles-m.css and once more to styles-l.css.

For LESS styles rules to be compiled to styles-m.css without a media query so that they apply to all screen widths use the @media-common style group separation.

//
//  Common (style-m.css)
//  _____________________________________________
& when (@media-common = true) {
    // your code
}

For grouping style rules in certain media queries the .media-width() mixin used.

.media-width(<@extremum>, <@break>);

@extremum: max|min - sets whether to use min-width or max-width in media query condition. If max is used the compiled styles will be placed in styles-m.css with the appropriate media query. Whereas if min is used the compiled styles will be placed in styles-l.css with the appropriate media query.

@break: value - sets the value of breakpoint to compare with in media query condition.

//
//  Mobile (style-m.css)
//  _____________________________________________
.media-width(@extremum, @break) when (@extremum = 'max') and (@break = @screen__s) {
    // your code
}

.media-width(@extremum, @break) when (@extremum = 'max') and (@break = @screen__m) {
    // your code
}

//
//  Desktop (style-l.css)
//  _____________________________________________
.media-width(@extremum, @break) when (@extremum = 'min') and (@break = @screen__m) {
    // your code
}

.media-width(@extremum, @break) when (@extremum = 'min') and (@break = @screen__l) {
    // your code
}

You can find more information about the Magento UI library responsive mixin usage in <your_Magento_instance>/pub/static/frontend/Magento/blank/en_US/css/docs/responsive.html (view in a browser).