<===> input.scss
.btn {
    .open& {
        color: #000;
    }
}

<===> error
Error: Invalid CSS after ".open": expected "{", was "&"
       
       "&" may only be used at the beginning of a compound selector.
        on line 2 of input.scss
  Use --trace for backtrace.

<===> error-dart-sass
Error: "&" may only used at the beginning of a compound selector.
  ,
2 |     .open&{
  |          ^
  '
  input.scss 2:10  root stylesheet