Mixins may not be defined within control directives or other mixins ?

[REPTILEHAUS]

trying to build this demo and keep hitting this issue

Module build failed: 
  @mixin pill-theme($bg: $nb-color-white, $txt: $nb-color-base-text) {
        ^
      Mixins may not be defined within control directives or other mixins.
      in /home/user/Development/user/nebula-components/nebula-components/components/_pills.scss (line 2, column 10)
 @ ./src/scss/main.scss 4:14-189
 @ ./src/index.jsx

[REPTILEHAUS]

and also ```ERROR in ./node_modules/css-loader!./node_modules/postcss-loader/lib??ref--2-2!./node_modules/sass-loader/lib/loader.js??ref--2-3!./src/scss/main.scss
Module build failed:
@function getLineHeight() {