Anchored container queries are not supported

[uandco]

This syntax is valid according to https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Anchor_positioning/Anchored_container_queries

@container anchored(fallback: flip-block flip-inline) {

Yet it's seen as a syntax error:

[lightningcss minify] Unexpected token Function("anchored")
1  |  ...:calc(var(--sp-l) + var(--sp-m) + var(--sp-xxs))}}@container anchored(fallback: flip-block flip-inline){...
   |                                      

Adding a space between anchored and ( eliminates the error (but also breaks the syntax and is ignored in the browser).
Still the argument with a double fallabck is causing issues:

[lightningcss minify] Unexpected token Ident("flip-inline")
1  |  ... + var(--sp-xxs))}}@container anchored(fallback: flip-block flip-inline){...
   |                                                                ^