Create a template
Templates → New template offers first Start from a layout: one of the five layouts of the gallery, in your brand, with the unsubscribe link, the preferences link and your postal address in its footer. Create the template saves it in one click and opens it in the HTML editor. Or choose An empty page, then an editor (blocks, Markdown, HTML or MJML), and Open the editor: give the template its name there. The editable zone is written:An example in HTML
Extra CSS
The Extra CSS field is folded into the e-mail as it is sent: the rules are copied intostyle attributes, and the media queries are kept in the header.