"The shadow of the mica screen is deep, the long river is gradually falling, and the stars are sinking." What do you mean?

Through the screen decorated with mica, the candle shadow gradually fades away. The milky way sank and the morning star disappeared. Chang 'e, a poem by Li Shangyin, a poet in the Tang Dynasty. Original: Chang 'e. Tang Li Shangyin. The mica screen was dyed red by thick candles, and the Milky Way gradually tilted towards the morning star. Chang 'e, I must regret eating the elixir, and now I am alone, in the blue sky, singing every night. Through the screen decorated with mica, the shadow of the candle gradually faded. The milky way sank and the morning star disappeared. Chang 'e regrets being lonely and stealing the elixir. Now only the blue sky and blue sea accompany her with a lonely heart every night.