Getting an error when trying to implement the CSS

[ESDUNCAN]

Keep on getting this error message:

ERROR in ./src/index.scss (./node_modules/css-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[7].use[1]!./node_modules/postcss-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[7].use[2]!./node_modules/resolve-url-loader/index.js??ruleSet[1].rules[1].oneOf[7].use[3]!./node_modules/sass-loader/dist/cjs.js??ruleSet[1].rules[1].oneOf[7].use[4]!./src/index.scss)
Module build failed (from ./node_modules/sass-loader/dist/cjs.js):
SassError: Undefined variable.
╷
4 │ $carbon--theme: $theme--g100;
│ ^^^^^^^^^^^^
╵
src/index.scss 4:17 root stylesheet

webpack compiled with 1 error

Tried looking around online but cannot find a solution