I believe this refers to "Page-margin boxes" , defined at https://drafts.csswg.org/css-page-3/#margin-boxes

Support for other paged media properties is already on the site at https://caniuse.com/#feat=css-paged-media

no no no, i think Page-margin boxes not only @page, and i need @top-center and so.

Chrome does support @page, like

@page {
  margin: 5cm;
}

but does not support "Page-margin boxes", like

@page {
  @top-center {
    content: "4422";
    background-color: red;
    border: black 5px solid;
    width: 5cm;
    height: 5cm;
  }
}

Played around in practice by trying to print pdf from chrome 67. And I failed. There is software like weasyprint that did produce the red boxes. Anyway, It's a nice detail to advertise.

I'm very surprised to see a lot of green on the @page page. The linked spec lists a lot of things that no browsers even come close to supporting -- page-margin-box-type and the like.

Seeing the green here for chrome implies full support, but it seems this is only tracking the actual @page and not everything else in the spec.... everyone I've seen has partial support at best.

@page margin boxes don't seem to be supported in any major browsers at this moment at all. So yeah, the green boxes in https://caniuse.com/#feat=css-paged-media are quite misleading.

Based on today's update to this issue in the Chromium issue tracker, page margin boxes are now supported in Chromium. I assume that means they'll be coming to Chrome soon