Responsive

Magento UI library provides a strong approach for working with media queries. It`s based on recursive call of .media-width() mixin defined anywhere in project but invoked in one place in lib/web/css/source/lib/_responsive.less. That's why in the resulting styles.css we have every media query only once with all the rules there, not a multiple calls for the same query.

To see the media queries work resize window to understand which breakpoint is applied.

<div class="example-responsive-block"> are applied. </div>

.example-responsive-block {
    padding: 10px;
}

.media-width(@extremum, @break) when (@extremum = 'max') and (@break = @screen__m) {
    .example-responsive-block {
        background: #ffc;
    }
    .example-responsive-block:before {
        content: 'Mobile styles ';
        font-weight: bold;
    }
}

.media-width(@extremum, @break) when (@extremum = 'min') and (@break = @screen__m) {
    .example-responsive-block {
        background: #ccf;
    }
    .example-responsive-block:before {
        content: 'Desktop styles ';
        font-weight: bold;
    }
}

Responsive mixins usage

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

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

@extremum: max|min - sets whether to use min-width or max-width in media query condition
@break: value - sets the value of breakpoint to compare with in media query condition.
For example

  .media-width(@extremum, @break) when (@extremum = 'max') and (@break = @screen__s) {
      your styles
  }

It will be complied to

  @media only screen and (max-width: 640px) {
      your styles
  }

 

Media query style groups separation variables

@media-common: true|false - sets whether to output common styles. For common styles every time you want to add some styles you should use

  & when (@media-common = true) {
      your styles
  }

@media-target: all|desktop|mobile - Sets target device for styles output

  & when (@media-target = 'mobile'),
  (@media-target = 'all') {
     @media only screen and (max-width: (@screen__xs - 1)) {
         .media-width('max', @screen__xs);
     }
 }

Gathering

Everything that you include in collector mixins above will go in place where they declarated. As example all

  .media-width(@extremum, @break) {
      your code
  }

Will go to

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

By default you can find it _responsive.less file in li  

Responsive breakpoints

In Magento UI library there are predefined variables for breakpoints.

  @screen__xxs: 320px;
  @screen__xs: 480px;
  @screen__s: 640px;
  @screen__m: 768px;
  @screen__l: 1024px;
  @screen__xl: 1440px;