Email branding & design
Each audience has its own look, set under Settings → Email branding—pen names are brands, so they don't share.
Two legitimate styles
Branding off (the default): your emails go out as clean, personal-looking notes—the way mail from a friend looks. Many authors' best-performing emails are exactly this. Formatting, buttons, and images all still work.
Branding on: your emails wear a shell—logo up top (linkable, banner or compact), your colors on links and buttons, a styled footer. The editor shows a live preview, and colors you leave blank are derived from your accent color so you can set one color and be done.
Whichever you choose, a reader-friendly plain-text version still travels with every email, and your signup pages wear the same branding so the whole path matches.
Font size
The font size control lives in the same card but works in both modes, because readability isn't branding. If your readership skews older, try 20–24px—several successful authors run their whole list at 24. Headings scale proportionally.