Generated by SassMeister.com.

SassMeister-input-HTML.html

<button class="btn">
  btn
</button>

SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.1)
// Compass (v0.13.alpha.10)
// ----

@charset "utf-8";
$res:480px;
@mixin media-screen($res:480px){
  @media only screen and (max-width:$res){
    @content;
  }  
}

/** 
 * 使用mixin 配合 @content
 */
  @include media-screen($res){
    body{
      width:200px;
    }
    .btn{
      height:200px;
    }
  }

SassMeister-output.css

@charset "UTF-8";
/** 
 * 使用mixin 配合 @content
 */
@media only screen and (max-width: 480px) {
  body {
    width: 200px;
  }

  .btn {
    height: 200px;
  }
}

SassMeister-rendered.html

<button class="btn">
  btn
</button>