CSS3 Variables output in compiled CSS

For subtheming Claro it would make it a lot easier if we could leave the CSS3 Variables also in the output – with the fallback of the HEX codes for older browsers like e.g. IE11. But with this Claro could be easily subthemed/customized for Client wishes.

e.g.

:root {
  --color-absolutezero: #003cc5;
}

.button {
  background-color: #003cc5;
  background-color: var(--color-absolutezero);
}