How to change backgound color of textblock on editing?

By default, in GoJs, when user tries to edit text in textblock of gojs, white background appears. I need to change this white color to some different color. How can I do that?

First, become familiar with TextEditingTool and HTMLInfo:

In particular, note that you want to modify HTMLInfo | GoJS API.

And you can get the default HTMLInfo at
TextEditingTool | GoJS API.

And like all tools, you can get the default TextEditingTool at ToolManager | GoJS API.

So one way to do it is to define your own CSS class:

  .myTextEditorCSSClass {
    background: magenta;

and then right after your Diagram initialization:

myDiagram = $(go.Diagram, ...)

var tool = myDiagram.toolManager.textEditingTool;
tool.defaultTextEditor.mainElement.className = "myTextEditorCSSClass";