What is the fine-grained topic of the following text: Activists said about a dozen of their leaders had been detained before Prime Minister Narendra Modi officially opened the tribute to Sardar Vallabhbhai Patel, with an air force jet flyover, helicopters showering flowers on the statue and fireworks in the green, orange and white national colours. Only return the topic.
The official opening of Sardar Vallabhbhai Patel's tribute by Prime Minister Narendra Modi and the detainment of activists.