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):

children.push(borderDiv);
  }
  children.push(html);
  return {
    name: "div",
    attributes,
    children,
  };
}
function fixTextIndent(styles) {
  const indent = getMeasurement(styles.textIndent, "0px");
  if (indent >= 0) {
    return;
  }
  const align = styles.textAlign || "left";
  if (align === "left" || align === "right") {
    const name = "margin" + (align === "left" ? "Left" : "Right");
    const margin = getMeasurement(styles[name], "0px");
    styles[name] = `${margin - indent}pt`;
  }
}
function getFonts(family) {
  if (family.startsWith("'")) {
    family = `"${family.slice(1, family.length - 1)}"`;
  } else if (family.includes(" ") && !family.startsWith('"')) {
    family = `"${family}"`;
  }