Generated by SassMeister.com.

input.scss

@mixin foo() {
    content: 'original';
}
@mixin foo() {
    content: 'overwritten';
}

.foo {
    @include foo();
}

output.css

.foo {
  content: "overwritten";
}

settings.json

{
  "sass": {
    "compiler": "dart-sass/1.32.12",
    "extensions": {},
    "syntax": "SCSS",
    "outputStyle": "expanded"
  },
  "autoprefixer": false
}