I'm trying to style a PDF invoice and I want to use CSS variables to not repeat the same thing over in the CSS code.

I've tried this code in simple HTML/CSS and it works:

:root {
	​--secondary-color: rgba(116, 212, 220, 0.3);
}

table.table-dates > thead > tr > th {
	​background-color: var(--secondary-color) !important;
}

But in the code for the invoice only this works:

table.table-dates > thead > tr > th {
	​background-color: rgba(116, 212, 220, 0.3) !important;
}

Can someone tell me if I'm doing something wrong or is this feature not supported in Odoo?