Dubai shuttered Expo 2020 with a colourful closing ceremony punctuated by fireworks on Thursday, leaving a multi-billion dollar mini-city in the desert and heightened expectations for future hosts. Six months after the delayed opening of the $7 billion, purpose-built site, Christina Aguilera, Nora Jones and cellist Yo-Yo Ma performed at the LCD-lit Al Wasl Dome, Expo’s centrepiece, as pyrotechnics lit up the sprawling site. Millions of people have flocked to Expo’s 192 country pavilions in its final days, pushing visit numbers over 23 million — not far off the 25 million targeted, despite the…