I have attached a simple example to show you how you can modify the default TimeBreakTemplate - this template is set through the Chat ItemTemplateSelector. In the example I've only applied background color, but you can customize it per your requirements.
I am going to update the ItemTemplateSelector topic in our documentation to include the default TimeBreakTemplate.
I hope I was of help. Let me know if I can assist with anything else.
Regards,
Yana
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