GoJs edit textblock showing white background

Hello ,
I am using Gojs Text block editable it showing white background

then I include the code texteditor.js having following code

// HTML + JavaScript text editor menu, made with HTMLInfo
// This is a re-implementation of the default text editor
// This file exposes one instance of HTMLInfo, window.TextEditor
// See also TextEditor.html
(function(window) {
  var textarea = document.createElement('textarea');
  textarea.id = "myTextArea";

  textarea.addEventListener('input', function(e) {
    var tool = TextEditor.tool;
    if (tool.textBlock === null) return;
    var tempText = tool.measureTemporaryTextBlock(this.value);
    var scale = this.textScale;
    this.style.width = 20 + tempText.measuredBounds.width * scale + 'px';
    this.style.height = 10 + tempText.measuredBounds.height * scale + "px";
    this.rows = tempText.lineCount;
  }, false);

  textarea.addEventListener('keydown', function(e) {
    var tool = TextEditor.tool;
    if (tool.textBlock === null) return;
    var keynum = e.which;
    if (keynum === 13) { // Enter
      if (tool.textBlock.isMultiline === false) e.preventDefault();
      tool.acceptText(go.TextEditingTool.Enter);
      return;
    } else if (keynum === 9) { // Tab
      tool.acceptText(go.TextEditingTool.Tab);
      e.preventDefault();
      return;
    } else if (keynum === 27) { // Esc
      tool.doCancel();
      if (tool.diagram !== null) tool.diagram.doFocus();
    }
  }, false);

  // handle focus:
  textarea.addEventListener('focus', function(e) {
    var tool = TextEditor.tool;
    if (tool.currentTextEditor === null) return;

    if (tool.state === go.TextEditingTool.StateActive) {
      tool.state = go.TextEditingTool.StateEditing;
    }

    if (tool.selectsTextOnActivate) {
      textarea.select();
      textarea.setSelectionRange(0, 9999);
    }
  }, false);

  // Disallow blur.
  // If the textEditingTool blurs and the text is not valid,
  // we do not want focus taken off the element just because a user clicked elsewhere.
  textarea.addEventListener('blur', function(e) {
    var tool = TextEditor.tool;
    if (tool.currentTextEditor === null) return;

    textarea.focus();

    if (tool.selectsTextOnActivate) {
      textarea.select();
      textarea.setSelectionRange(0, 9999);
    }
  }, false);


  var TextEditor = new go.HTMLInfo();

  TextEditor.valueFunction = function() { return textarea.value; }

  TextEditor.mainElement = textarea; // to reference it more easily

  // used to be in doActivate
  TextEditor.show = function(textBlock, diagram, tool) {
    if (!(textBlock instanceof go.TextBlock)) return;

    TextEditor.tool = tool;  // remember the TextEditingTool for use by listeners

    // This is called during validation, if validation failed:
    if (tool.state === go.TextEditingTool.StateInvalid) {
      textarea.style.border = '3px solid red';
      textarea.focus();
      return;
    }

    // This part is called during initalization:

    var loc = textBlock.getDocumentPoint(go.Spot.Center);
    var pos = diagram.position;
    var sc = diagram.scale;
    var textscale = textBlock.getDocumentScale() * sc;
    if (textscale < tool.minimumEditorScale) textscale = tool.minimumEditorScale;
    // Add slightly more width/height to stop scrollbars and line wrapping on some browsers
    // +6 is firefox minimum, otherwise lines will be wrapped improperly
    var textwidth = (textBlock.naturalBounds.width * textscale) + 6;
    var textheight = (textBlock.naturalBounds.height * textscale) + 2;
    var left = (loc.x - pos.x) * sc;
    var top = (loc.y - pos.y) * sc;

    textarea.value = textBlock.text;
    // the only way you can mix font and fontSize is if the font inherits and the fontSize overrides
    // in the future maybe have textarea contained in its own div
    diagram.div.style['font'] = textBlock.font;

    var paddingsize = 1;

    textarea.style.cssText =
    'position: absolute;' +
    'z-index: 100;' +
    'font: inherit;' +
    'fontSize: ' + (textscale * 100) + '%;' +
    'lineHeight: normal;' +
    'width: ' + (textwidth) + 'px;' +
    'height: ' + (textheight) + 'px;' +
    'left: ' + ((left - (textwidth / 2) | 0) - paddingsize) + 'px;' +
    'top: ' + ((top - (textheight / 2) | 0) - paddingsize) + 'px;' +
    'textAlign: ' + textBlock.textAlign + ';' +
    'margin: 0;' +
    'padding: ' + paddingsize + 'px;' +
    'border: 0;' +
     'color: white;' +
    'background:black;'+
    'outline: none;' +
    'white-space: pre-wrap;' +
    'overflow: hidden;' // for proper IE wrap

    textarea.textScale = textscale; // attach a value to the textarea, for convenience

    // Show:
    diagram.div.appendChild(textarea);

    // After adding, focus:
    textarea.focus();
    if (tool.selectsTextOnActivate) {
      textarea.select();
      textarea.setSelectionRange(0, 9999);
    }
  };

  TextEditor.hide = function(diagram, tool) {
    diagram.div.removeChild(textarea);
    TextEditor.tool = null;  // forget reference to TextEditingTool
  }

  window.TextEditor = TextEditor;
})(window);
exports.customTextEditor = window.TextEditor;

using in my component
import {customTextEditor} from './script/TextEditor.js'; 

and used this code

this.myDiagram.toolManager.textEditingTool.defaultTextEditor = customTextEditor;

it is able to change the backgound color as per my requirement but editing this text box giving error which causing my Gojs unstable
any suggestion?

What is the error? In general, we cannot debug your code for you.

If you want to see an example of changing the editor to show a different color background: How to change backgound color of textblock on editing?