<===> input.scss
a:nth-child() {
  color: yellowgreen;
}

<===> error
Error: Invalid CSS after "a:nth-child(": expected An+B expression, was ")"
        on line 2 of input.scss
  Use --trace for backtrace.

<===> error-libsass
Error: Invalid CSS after "a:nth-child(": expected An+B expression, was ") {"
        on line 1:3 of input.scss
>> a:nth-child() {
   --^

<===> error-dart-sass
Error: Expected "n".
  ,
1 | a:nth-child(){
  |             ^
  '
  input.scss 1:13  root stylesheet