Incorrect positioning in page area with @page with padding

[MurakamiShinyu]

Absolute-positioned elements are positioned incorrectly in the page area with @page with non-zero padding. The page area that is the initial containing block must be the content box of the page box, but it seems that the absolute-positioned elements are positioned as if the initial containing block is the padding box of the page box.

Example:

<style>
@page {
  size: 500px;
  margin: 50px;
  border: 10px dotted blue;
  padding: 40px;
}
* {
  margin: 0;
}
.absolute-box {
  position: absolute;
  top: 0;
  right: 0;
  width: 150px;
  height: 150px;
  background: magenta;
}
.static-box {
  width: 150px;
  height: 150px;
  background: orange;
}
</style>
<div class="absolute-box">Absolute</div>
<div class="static-box">Static</div>

(page-area-padding-position.html)

Test with Vivliostyle Viewer (v2.31.0):

• https://vivliostyle.github.io/viewer/v2.31.0/#src=https://gist.githack.com/MurakamiShinyu/3d217c7c3d32636a007a5737a7fa44fd/raw/page-area-padding-position.html

Screenshot:

Expected result:
(This is a screenshot of the same HTML file rendered in Chrome's print preview.)

---

This problem is not only with the absolute positioning but also with page floats and footnotes.

Example: page-box-padding-test.html

Test with Vivliostyle Viewer (v2.31.0):

• https://vivliostyle.github.io/viewer/v2.31.0/#src=https://gist.githubusercontent.com/MurakamiShinyu/3d217c7c3d32636a007a5737a7fa44fd/raw/page-box-padding-test.html

Screenshot:

Extected result:
(This is a screenshot of the same HTML+CSS rendered by Antenna House Formatter using https://printcss.live/editor.)