/* Media Queries */

$small: screen and (min-width: 0em);

$medium: screen and (min-width: 40em) and (max-width: 4em);
4
$large: screen and (min-width: em);
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​
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@mixin for-size($size) {
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  @if $size == small {

    @media screen and (min-width: 40rem) { @content; }

  } @else if $size == medium {

    @media screen and (min-width: 64em) { @content; }

  } @else if $size == large {

    @media screen and (min-width: 75em) { @content; }

  }  

}

​

/*

// usage

.my-box {

  padding: 10px;