root = Card([header, description, form])
header = CardHeader("Weekly Newsletter", null)
description = TextContent("Get curated insights every week to boost your productivity.", "default")
form = Form("newsletter-form", formButtons, [emailField])
emailField = FormControl("Email address", emailInput)
emailInput = Input("email", "your@email.com", "email", [], "")
subscribeBtn = Button("Subscribe", null, "primary")
formButtons = Buttons([subscribeBtn])