<===> input.scss
// Arguments passed to @content blocks are lexically-scoped within those blocks.

$var: top-level;

@mixin mixin($var) {
  mixin-var-before: $var;
  @content(content-argument);
  mixin-var-after: $var;
}

@mixin inner {
  var-in-inner: $var;
}

scope {
  var-before: $var;
  @include mixin(mixin-argument) using ($var) {
    content-var-before: $var;
    @include inner;
    content-var-after: $var;
  }
  var-after: $var;
}

<===> output.css
scope {
  var-before: top-level;
  mixin-var-before: mixin-argument;
  content-var-before: content-argument;
  var-in-inner: top-level;
  content-var-after: content-argument;
  mixin-var-after: mixin-argument;
  var-after: top-level;
}