Undefined variable: "$text-color"

[pwab]

When using the custom.scss file in the exampleSite directory I receive the following error while building:

Error: error building site:
    TOCSS: failed to transform "/css/custom.scss" (text/x-scss): "/.../assets/css/custom.scss:37:26":
    Undefined variable: "$text-color".

It seems the $text-color variable is not set before the custom scss is compiled or some import is missing. I solved this by adding $text-color: #000000; at the top of custom.scss but I'm not sure if this is the right solution.