How do you set alternating colors in the list of topics

Development
6

Sure!
Can you tell me why I cannot use $primary-low in the theme component? It’s used all over the place in core (e.g. as the background color of buttons), and I think it’s a good color for the darkened rows, but it’s undefined:

Error: Undefined variable: "$primary-low".
        on line 2 of theme_field.scss
>>     background-color: $primary-low;
   ----------------------^