Maxime Brazeilles developed CSS formatting support for the MJML <mj-style> tag in the prettier/prettier repository, enabling consistent styling within MJML email templates. He extended the parsing and printing pipeline to recognize and format CSS embedded in <mj-style>, ensuring that email template styles are both readable and maintainable. Using JavaScript and front end development skills, Maxime introduced comprehensive tests to validate the new formatting behavior and safeguard against regressions, maintaining backward compatibility with existing rules. His work addressed a specific formatting gap for MJML users, reducing manual effort and improving the overall consistency of styled email templates.