I am making a demonstration of @property and want to show a banner if the viewer’s browser does not support @property. Normally I would do something like this (in this example, hiding the banner if color-mix is supported):

@supports (color: color-mix(in srgb, red, tan)) {
  .unsupported-banner {
    display: none;
  }
}

However the MDN documentation for @supports does not mention a way of testing at-rules. Neither of the following work:

• @supports (@property) {...}
• @supports (syntax: "<number>") {...}

So the question is, is this possible in CSS?