You need to bring your developers and designer together early in the process. If you don’t do this they will cause issues for each other and blow out your projects. Your designer’s ideas for the UI and UX include little details that are sometimes not documented well like hovers and transitions and simple animations. These details when omitted affects the estimates and effort that a developer needs to complete a feature.
Bring them in early have them collaborate and be on the same page, this will ensure a smoother project experience.