root = Card([header, description, form])
header = CardHeader("The Product Weekly", "One email every Tuesday")
description = TextContent("Get one actionable product insight, a curated link, and a community highlight — in under 5 minutes.")
form = Form("newsletter-signup", formButtons, [emailField])
emailField = FormControl("Email address", emailInput, "We'll never share your email.")
emailInput = Input("email", "you@example.com", "email")
formButtons = Buttons([subscribeBtn])
subscribeBtn = Button("Subscribe", null, "primary")