Property container doesn't exist

[PitWenkin]

main, aside {
  container: my-layout / inline-size;
}

from https://www.w3.org/TR/css-contain-3/#container-queries is not recognized as valid. Returns Property container doesn't exist. The closest matching property name is contain : my-layout / inline-size

Neither is

main, aside {
  container-name: my-layout;
  container-type: inline-size;
}

Returns Property container-name doesn't exist : my-layout Property container-type doesn't exist : inline-size