Attach (recommended) or Link to PDF file here:
[Erstattung von Arbeitgeberaufwendungen nach __ 56 Abs. 1 und 57, 58 Infektionsschutzgesetz - Antrag(1).pdf](https://github.com/mozilla/pdf.js/files/6009589/Erstattung.von.Arbeitgeberaufwendungen.nach.__.56.Abs.1.und.57.58.Infektionsschutzgesetz.-.Antrag.1.pdf)

Also available at: [formularserver.bayern.de](https://formularserver.bayern.de/intelliform/forms/stmi+regierungen/rof/b5/55.2/rof_55.2-086/index)

Configuration:
- Web browser and its version: FF 85.0.2 and FF 86.0b9
- Operating system and its version: Win 10
- PDF.js version: 
FF 85.0.2:
const pdfjsVersion = '2.7.345';
const pdfjsBuild = 'b194c820b';

FF 86.0b9:
const pdfjsVersion = '2.7.510';
const pdfjsBuild = '631bada0d';

- Is a browser extension:
no
Steps to reproduce the problem:
1. load pdf document

What is the expected behavior? (add screenshot)
This is with latest Chrome:
![grafik](https://user-images.githubusercontent.com/584660/108499622-e2360880-72ae-11eb-82a7-b181619ff079.png)


What went wrong? (add screenshot)
The checkboxes for e.g. "Geschlecht" are black and you cannot see which one is checked. But this is true for every checkbox in that document.
![grafik](https://user-images.githubusercontent.com/584660/108499753-14e00100-72af-11eb-89d3-1f5ca652e058.png)

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

if (blurListener) {
        element.addEventListener("blur", blurListener);
      }
      if (this.data.maxLen !== null) {
        element.maxLength = this.data.maxLen;
      }
      if (this.data.comb) {
        const fieldWidth = this.data.rect[2] - this.data.rect[0];
        const combWidth = fieldWidth / this.data.maxLen;
        element.classList.add("comb");
        element.style.letterSpacing = `calc(${combWidth}px - 1ch)`;
      }
    } else {
      element = document.createElement("div");
      element.textContent = this.data.fieldValue;
      element.style.verticalAlign = "middle";
      element.style.display = "table-cell";
    }
    this._setTextStyle(element);
    this.container.appendChild(element);
    return this.container;
  }
  /**
   * Apply text styles to the text in the element.
   *
   * @private
   * @param {HTMLDivElement} element
   * @memberof TextWidgetAnnotationElement
   */
  _setTextStyle(element) {