root = Card([header, description, form])
header = CardHeader("The Weekly Build", "One email, every Friday")
description = TextContent("Get one actionable product insight, one useful tool, and one great read — in under 5 minutes, every week.")
form = Form("newsletter-signup", formButtons, [emailField])
emailField = FormControl("Email address", emailInput, "We respect your inbox. No spam, ever.")
emailInput = Input("email", "you@example.com", "email")
formButtons = Buttons([subscribeBtn])
subscribeBtn = Button("Subscribe", null, "primary")