How To: SharePoint grouped view conditional formatting

Recently my customer asked me to create a dashboard, to monitor completion of tasks in a workflow. The idea was to highlight completed, on track and overdue tasks with different colors. First I thought about using SharePoint list with Modern Experience, and column formatting. But then I was asked, not only to highlight rows for tasks, but also their grouping header – as there were many tasks created per each group of tasks and the customer wanted to see status of a whole group ad-hoc, without a need to drill down.