Using your own variables for global colors in generatePress

Hi,
I have defined my own variables for colors in additional CSS, e.g.

:root {
     --hellgrau-color: rgba(217,217,217,1);
     --grau_1-color: rgba(190,190,190,1);
     --grau_2-color: rgba(204,204,204,1);
     --blau-color: rgba(11,48,67,1);
     --tuerkis-color: rgba(0,255,255,1);
}

However, if I want to use these variables in the Customizer at Global Colors, this is unfortunately not possible. Of course I can enter the color codes without any problems, but I would rather use the variables.
Is there a way to do this or maybe even use a theme.json in the context (I know that theme.json is used first with block themes).
I had already looked at the following post: https://generatepress.com/generatepress-3-1-global-colors-dynamic-typography/
Thanks for advice.
Best regards,
Hans-Gerd