The central idea is what the main thing. For this, I think the central idea is simply Cactuses.
I'm not sure what another supporting detail can be, but if there's a back side, or another page about cactuses, I can sure help! But if that's the only side, ask your parents. xD
Answer:
Im pretty sure those are the instructions.
....
Whats your question??
Answer:
it looks like it is a city with many thing such as trucks driving by, and many colorful lights
Explanation: