CSS: @page

I like this plugin very much. Thanks a lot!

Now I am trying to set up my own custom CSS for pdf and printing: everything fine except @page: no reactions to anything I try.

Example: Inside the CSS-Field (printing), I wrote:

@page {
    size: auto;
    margin: 25mm 25mm 20mm 25mm;
    orphans: 4;
    widows: 2;
}

No reaction, margins are still very small.
Probably I am just stupid.
Thanks for a hint.

https://wordpress.org/plugins/read-offline/