nested-mixin.scss

@mixin mix1{
    font-size: 12px;
}

@mixin mix2{
  @include mix;
  color: blue;
}

@mixin mix3{
  @include mix2;
  color: red;
  border: 1px solid red;
}

@mixin mix4{
  @include mix3;
  color: green;
  border: 3px solid green;
}

.style{
    font-size: 14px;
}
.style{
    @include mix4;
}
.style2{
    @extend .style;
    background: red;
}