root = Card([header, amountSection, dueDateSection, paySection], "card", "column", "l")
header = CardHeader("Invoice #INV-2024-001", "Acme Corporation")
amountSection = Card([amountLabel, amountValue], "sunk", "column", "m", "center")
amountLabel = TextContent("Amount Due", "small-heavy")
amountValue = TextContent("$12,450.00 USD", "large-heavy")
dueDateSection = Card([dueLabel, dueValue], "clear", "row", "m", "center", "center")
dueLabel = TextContent("Due Date:", "default")
dueValue = TextContent("March 15, 2024", "large-heavy")
paySection = Buttons([payBtn], "column")
payBtn = Button("Pay Now", null, "primary", "normal", "large")