<===> input.scss
.bar {
  @extend .foo;
  color: green;
}
<===> error
Error: ".bar" failed to @extend ".foo".
       The selector ".foo" was not found.
       Use "@extend .foo !optional" if the extend should be able to fail.
        on line 2 of input.scss
  Use --trace for backtrace.

<===> error-libsass
Error: The target selector was not found.
       Use "@extend .foo !optional" to avoid this error.
        on line 2 of input.scss
>>   @extend .foo;
   ----------^

<===> error-dart-sass
Error: The target selector was not found.
Use "@extend .foo !optional" to avoid this error.
  ,
2 |   @extend .foo;
  |   ^^^^^^^^^^^^
  '
  input.scss 2:3  root stylesheet