1. @mixin alert1 {
    2.   color: #000;
    4.   background: {
    5.     color: #fff;
    6.   }
    8.   a {
    9.     font-size: 15px;
    10.     text-decoration: none;
    11.   }
    12. }
    14. div {
    15.   @include alert1;
    16. }
    18. @mixin alert2($color, $size) {
    19.   color: $color;
    20.   font-size: $size;
    22.   a {
    23.     // color: darken($color: #000000, $amount: 0);
    24.     color: darken($color, 10%);
    25.   }
    26. }
    28. p {
    29.   @include alert2($size: 18px, $color: #fff);
    30.   // @include alert2(#fff, 18px);
    31. }
    div {
  color: #000;
  background-color: #fff;
}

div a {
  font-size: 15px;
  text-decoration: none;
}

p {
  color: #fff;
  font-size: 18px;
}

p a {
  color: #e6e6e6;
}