SassError 90var--num is not a number ╷81 │ for $val from 1 to $num

This error is caused by attempting to use a CSS variable as a numerical value in a Sass loop.

To fix the error, you need to make sure that the variable --num is defined as a number before using it in the loop. You can do this by either setting it explicitly as a number in your CSS, or by converting it to a number in your Sass code using the to-number() function.

For example, if you want --num to be the number 10, you can define it in your CSS like this:

:root {
  --num: 10;
}

Or, if --num is defined as a string in your CSS, you can convert it to a number in your Sass code like this:

$num: to-number(var(--num));

This will ensure that $num is treated as a number in your loop and prevent the SassError: 90var(--num) is not a number error from occurring.