root = Card([header, intro, form, note])
header = CardHeader("Product Weekly", "The best product news, every Tuesday")
intro = TextContent("Get one curated email each week with the top launches, essays, and tools.")
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")
note = TextContent("Unsubscribe anytime. No spam, ever.", "small")