Why are the values ​​not written to scss?

Question

Sass

Hello. For the life of me, I don't understand why this post is incorrect.

@mixin placeholder {
  &::-webkit-input-placeholder,
  &::-moz-placeholder ,
  &:-ms-input-placeholder, 
  &:-moz-placeholder {
    color: rgba(0, 0, 0, 0.5);
  }
}

Answer 1

had to put a mixin inside another mixin