printing - CSS to set A4 paper size

Question

I need simulate an A4 paper in web and allow to print this page as it is show on browser (Chrome, specifically). I set the element size to 21cm x 29.7cm, but when I send to print (or print preview) it clip my page.

See this Live example!

body {
  margin: 0;
  padding: 0;
  background-color: #FAFAFA;
  font: 12pt "Tahoma";
}

* {
  box-sizing: border-box;
  -moz-box-sizing: border-box;
}

.page {
  width: 21cm;
  min-height: 29.7cm;
  padding: 2cm;
  margin: 1cm auto;
  border: 1px #D3D3D3 solid;
  border-radius: 5px;
  background: white;
  box-shadow: 0 0 5px rgba(0, 0, 0, 0.1);
}

.subpage {
  padding: 1cm;
  border: 5px red solid;
  height: 256mm;
  outline: 2cm #FFEAEA solid;
}

@page {
  size: A4;
  margin: 0;
}

@media print {
  .page {
    margin: 0;
    border: initial;
    border-radius: initial;
    width: initial;
    min-height: initial;
    box-shadow: initial;
    background: initial;
    page-break-after: always;
  }
}

<div class="book">
  <div class="page">
    <div class="subpage">Page 1/2</div>
  </div>
  <div class="page">
    <div class="subpage">Page 2/2</div>
  </div>
</div>

Answer 1

I looked into this a bit more and the actual problem seems to be with assigning initial to page width under the print media rule. It seems like in Chrome width: initial on the .page element results in scaling of the page content if no specific length value is defined for width on any of the parent elements (width: initial in this case resolves to width: auto ... but actually any value smaller than the size defined under the @page rule causes the same issue).

So not only the content is now too long for the page (by about 2cm), but also the page padding will be slightly more than the initial 2cm and so on (it seems to render the contents under width: auto to the width of ~196mm and then scale the whole content up to the width of 210mm ~ but strangely exactly the same scaling factor is applied to contents with any width smaller than 210mm).

To fix this problem you can simply in the print media rule assign the A4 paper width and hight to html, body or directly to .page and in this case avoid the initial keyword.

DEMO

@page {
  size: A4;
  margin: 0;
}
@media print {
  html, body {
    width: 210mm;
    height: 297mm;
  }
  /* ... the rest of the rules ... */
}

^{This seems to keep everything else the way it is in your original CSS and fix the problem in Chrome (tested in different versions of Chrome under Windows, OS X and Ubuntu).}