root = Card([header, attendeesText, joinBtn])
header = CardHeader(meetingTitle, meetingTime)
attendeesText = TextContent("Attendees: Alice, Bob, Charlie")
joinBtn = Button("Join Call", "https://example.com/join/123", "primary", "medium")
meetingTitle = "Project Sync"
meetingTime = "2025-10-01 10:00 AM"