@document

@document url("https://www.example.com/") {
  h1 {
    color: green;
  }
}

@document [ <url> | url-prefix(<string>) | domain(<string>) | regexp(<string>) ]# {
  <group-rule-body>
}

@document url(http://www.w3.org/),
          url-prefix(http://www.w3.org/Style/),
          domain(mozilla.org),
          regexp("https:.*") {
  /* CSS rules here apply to:
     - The page "http://www.w3.org/"
     - Any page whose URL begins with "http://www.w3.org/Style/"
     - Any page whose URL's host is "mozilla.org"
       or ends with ".mozilla.org"
     - Any page whose URL starts with "https:" */

  /* Make the above-mentioned pages really ugly */
  body {
    color: purple;
    background: yellow;
  }
}