SVG radius or position with CSS variables

Question

Is it possible to use CSS Variables in SVG to manipulate values like radius or position in the "attribute styles" of an element?

For Example, in the below code, I have added a CSS color variable - --dark-text-clr and a radius variable --radius. When I use the color CSS variable in fill it renders fine - 1st circle, but using the radius variable doesn't render the element - 2nd circle.

:root{
--dark-text-clr: blue;
--radius: 12;
}

<svg xmlns="http://www.w3.org/2000/svg" width="300px" height="100px" viewBox="0 0 300 100">
  <circle cx="9" cy="9" fill="var(--dark-text-clr)" mask="url(#moon-mask)" r=9 ></circle>
  <circle cx="36" cy="20" fill="var(--dark-text-clr)" mask="url(#moon-mask)" r="var(--radius)" ></circle>
</svg>

Answer 1

Yes, but CSS must have units for non-zero values.

:root{
--dark-text-clr: blue;
--radius: 12px;
}

<svg xmlns="http://www.w3.org/2000/svg" width="300px" height="100px" viewBox="0 0 300 100">
  <circle cx="9" cy="9" fill="var(--dark-text-clr)" mask="url(#moon-mask)" r=9 ></circle>
  <circle cx="36" cy="20" fill="var(--dark-text-clr)" mask="url(#moon-mask)" r="var(--radius)" ></circle>
</svg>