Firstly, thank you for your interest in contributing to our tutorials. We use Jekyll + Markdown for our documentation. To contribute, simply make a pull request (PR) with changes in the Markdown files ...

,date_trunc('month',date)::date as first_day_of_month ,(date_trunc('month',date) + interval '1 month' - interval '1 day')::date as last_day_of_month ...