root = Card([header, form])
header = CardHeader("The Weekly Build", "One email every Friday — a short rundown of the best product, design, and engineering reads we found this week. No fluff, no spam, unsubscribe anytime.")
form = Form("newsletter-signup", formButtons, [emailField])
emailField = FormControl("Email address", emailInput, "We'll only send you the newsletter, never anything else.")
emailInput = Input("email", "you@example.com", "email")
formButtons = Buttons([subscribeBtn])
subscribeBtn = Button("Subscribe", null, "primary")