This project can help you to kick start an email template layout.
Templates located at /templates folder, and each template has it's own .css file. Change the template layout and css file, and run npm run build command to get your email template built with css inlined.
Alternatively, you can run npm start command to see your changes in browser. While npm start is running, open the template file from build folder in the browser and modify files within this folder. To see your changes reload the browser.