CSS variable calculation of HSL values

Question

I want to have a basic HSL color value which I want to implement as a gradient as follows:

:root {
    --hue: 201;
    --saturation: 31;
    --lightness: 40; 
    --mainColor: hsl(var(--hue),var(--saturation),var(--lightness));

    --difference: 20; /* 0 + --difference < --lightness < 100 - --difference */

    --lightnessPlus: calc(var(--lightness) + var(--difference));
    --colorFrom: hsl(var(--hue),var(--saturation),var(--lightnessPlus));

    --lightnessMinus: calc(var(--lightness) - var(--difference));
    --colorTo: hsl(var(--hue),var(--saturation),var(--lightnessMinus));
}

[...]
.class {
    background-image: linear-gradient(to right, var(--colorFrom), var(--colorTo));
}

The above code produces a transparent object and I fail to comprehend why, please help!

Answer 1

You are missing percentages. the syntax should be hsl(h, s%, l%) (https://www.w3.org/TR/css-color-3/)

:root {
    --hue: 201;
    --saturation: 31%; /* here */
    --lightness: 40; 
    --mainColor: hsl(var(--hue),var(--saturation),var(--lightness));

    --difference: 20;

    --lightnessPlus: calc((var(--lightness) + var(--difference))*1%); /* here */
    --colorFrom: hsl(var(--hue),var(--saturation),var(--lightnessPlus));

    --lightnessMinus: calc((var(--lightness) - var(--difference))*1%);  /* here */
    --colorTo: hsl(var(--hue),var(--saturation),var(--lightnessMinus));
}

body {
    background-image: linear-gradient(to right, var(--colorFrom), var(--colorTo));
}

Or

:root {
    --hue: 201;
    --saturation: 31%; /* here */
    --lightness: 40%; /* here */
    --mainColor: hsl(var(--hue),var(--saturation),var(--lightness));

    --difference: 20%; /* here */

    --lightnessPlus: calc(var(--lightness) + var(--difference)); 
    --colorFrom: hsl(var(--hue),var(--saturation),var(--lightnessPlus));

    --lightnessMinus: calc(var(--lightness) - var(--difference)); 
    --colorTo: hsl(var(--hue),var(--saturation),var(--lightnessMinus));
}

body {
    background-image: linear-gradient(to right, var(--colorFrom), var(--colorTo));
}