Error > stdin:253
argument `$color` of `darken($color, $amount)` must be a color

Backtrace:
	stdin:253, in function `darken`
	stdin:253
    @include transition(all 0.2s ease-out);
    &:hover,
    &:focus {
        background-color: $colorBorder;
    }
    &:active {
        background-color: darken($colorBorder, 10%);
    }
}

.js-qty__adjust--plus {
    right: 0;
    border-left: 1px solid $colorBorder;
}