渐进增强：Build pages for low-level browsers to ensure the most basic functions, and then improve and add functions such as effects and interactions for advanced browsers to achieve a better user experience. 优雅降级：Build a complete function from the beginning, and then make it compatible with low-level browsers.
区别：Elegant downgrading starts from the complicated status quo and attempts to reduce the supply of user experience, while incremental enhancement starts from a very basic, functional version and continues to expand to meet the needs of future environments. Degradation (decay in function) means looking back; while progressive enhancement means looking forward, while ensuring that its foundation is in a safe place.
