Sass混入

@mixin demo-1{
  width:50px;
}
div{
  @include demo-1;
}

div{
  width:50px;
}

@mixin demo-1{
  a{
    width:50px;
  }
}
div{
  @include demo-1;
}

div{
  a{
    width:50px;
  }
}