Attach (recommended) or Link to PDF file here:

Configuration:
- Web browser and its version: Firefox 88.0.1
- Operating system and its version: Windows 10.0.19043.985]
- PDF.js version: (commit 706c27b9d4b3b9ff6fc3de82bcf71a0610604a1c) (also tested pr/13473 at 296bbdc4)
- Is a browser extension: N/A

Steps to reproduce the problem:
1. Enable experimental XFA
2. Open PDF
[dir2020-02_form.pdf](https://github.com/mozilla/pdf.js/files/6571084/dir2020-02_form.pdf)

What is the expected behavior? (add screenshot)
Margins of `subforms` (e.g. *General_Election_Information*, *General_Information_Other*) are honored.
![image](https://user-images.githubusercontent.com/7104454/120212605-32066300-c200-11eb-9c66-f2d05c9451ec.png)
What went wrong? (add screenshot)
Margins are not honored. 
![image](https://user-images.githubusercontent.com/7104454/120212535-1ac77580-c200-11eb-8332-9924602ef991.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

position: "absolute",
      });
      const wrapper = page1.children[1];
      const draw = wrapper.children[0];
      expect(wrapper.attributes.class).toEqual("xfaWrapper");
      expect(wrapper.attributes.style).toEqual({
        left: "2px",
        position: "absolute",
        top: "1px",
      });
      expect(draw.attributes.class).toEqual("xfaDraw xfaFont");
      expect(draw.attributes.style).toEqual({
        color: "#0c1722",
        fontFamily: "FooBar",
        fontSize: "6.93px",
        height: "22px",
        padding: "1px 4px 2px 3px",
        transform: "rotate(-90deg)",
        transformOrigin: "top left",
        verticalAlign: "2px",
        width: "11px",
      });
      
      expect(draw.attributes.style).toEqual(
        pages.children[1].children[1].children[0].attributes.style
      );
    });
  });
});