How to ignore/supress parcel error about new CSS feature?

Question

I'm new to Parcel, and am getting this error:

@parcel/transformer-css: Unknown at rule: @property

in relation to this CSS block

@property --a {
  syntax: '<angle>';
  inherits: false;
  initial-value: 0deg;
}

which is new enough that it's not yet supported in Firefox.

https://developer.mozilla.org/en-US/docs/Web/CSS/@property

How can I ignore/suppress this error?