Insomnia is one of the most common sleep disorders and affects approximately 10 - 40% of the population across different age groups in Hong Kong. Our previous study has shown that insomnia can be prevented through a brief cognitive behavioral prevention program in adolescents. However, there is very limited data in the adult population. Current study aims to evaluate a digital sleep-focused platform which consists of different intervention plan according to user's insomnia severity level and employed a stepped care model. Thus, the effectiveness of the stepped care model will be evaluated in a real world setting using stepped wedge cluster randomized controlled design to evaluate potential preventive effect on adults who only with mild insomnia symptoms. The program will be rolled out to different districts in Hong Kong sequentially in 18 districts over 4 steps with a equally spaced time periods. The primary aim of this study is to evaluate the effects of a stepped-care CBT-I model in improving sleep and prevent the incidence of insomnia among participants with mild insomnia.