What is "soursweet"

Soursweet is a 1988 British film directed by Mike Newell. The story, set in the 1960s, is a comedy drama about a young Hong Kong Chinese couple who emigrate to England and start a family. Initially Chen works long hours in a Chinese restaurant while his wife Lily looks after their baby, dreaming of the day when they can open their own business. When Chen becomes indebted to Triads through gambling he decides it is time for his family to go it alone. The screenplay was written by Ian McEwan from the novel Sour Sweet by Timothy Mo.