What you can change, and what you cannot

The script embed exposes two attributes, and takes its colour and font from your branding. That is the whole of it: no themes, no layout switch, no way to reword the button, and no stylesheet to override.

If that is not enough, the answer is not a setting. It is to write the form yourself and post it to Issue Mint, which is what the plain HTML form is for and costs nothing extra.

The two attributes

data-issuemint marks a container. Any element carrying it becomes a subscribe form, and several on one page each get their own.

data-key goes on the script tag and names your newsletter. Those two are the entire interface. The script reads no other attribute, so a data-theme or a data-button-label you invent is ignored rather than being an error you can debug. One more attribute turns up in your markup without you writing it: data-issuemint-ready, which the script stamps on a container it has already mounted so a second copy of the script cannot render the form twice.

What comes from your branding

Two things reach the form: your primary colour and your body font. Both are set in Settings, then Branding, and are described in full under branding your newsletter.

The colour becomes the button background and the focus outline on the field. It has to be a six-digit hex value, which the colour picker always produces, and anything else falls back to Issue Mint’s own green. The body font is named ahead of a system fallback stack, and because the script downloads no font files it applies where your page already loads that font.

Nothing else in Branding appears in the form. Your logo and your heading font are used on your website and in your issues, not here.

What stays fixed

The label reads Email address. The placeholder reads you@example.com. The button reads Subscribe, and Subscribing… while it works. The form is a single row that wraps on a narrow screen, at most 26rem wide, and every message a reader sees after submitting is Issue Mint’s wording.

None of that is configurable. The class names those elements hang off are namespaced so your site’s own form styles cannot bleed into them, but they are an implementation detail rather than a documented interface, so writing CSS against them is not something Issue Mint tests or undertakes to keep working.

A form of your own

Your own markup posted to the f/ address in the plain snippet is the supported way to have a form that looks nothing like the embedded one. Style it however you like, because Issue Mint never sees the markup.

The fields it reads are email, which is required and up to 255 characters, first_name, which is optional and up to 120, and the honeypot, which has to arrive empty or not at all. Everything else you post is ignored, so extra fields of your own are harmless but are not stored.

If you want your own design and the in-place confirmation, your JavaScript can post to the endpoint the script embed uses: POST https://app.issuemint.com/api/embed/{your key}/subscribe, with a JSON body carrying email, from any origin. It answers 200 with a message to show the reader, 422 with errors keyed by field, and 429 once the per-IP limit is reached. You take on the error handling and nothing else changes.

Or use the form on your own website

Every newsletter gets a website with a subscribe form on it from the day you sign up, and that form takes its own styling from the website’s theme rather than from the embed.

There is nothing to paste and nothing to maintain, so if the page you were about to embed a form into is a landing page you have not built yet, this is the shorter road. A link to your newsletter’s own address collects signups perfectly well.

Which route to take

Paste the script if you want two lines that match your colours and confirm without leaving the page. Use the plain HTML form if the page cannot run JavaScript, or if you want the markup and the styling to be yours. Post to the endpoint yourself if you want both your own design and an answer shown in place. Send people to your own newsletter website if you would rather not touch another site at all.