Hey there. So it's time to actually build your high fidelity, high res mock-up. There are a few different tools to use. The most popular are XD, which is Adobe's Experience Designer. There is Sketch, another super popular one. There's other ones like Framer and Azure, InVision Studio.
A lot of people also use just plain old Photoshop and Illustrator to do the UI, and they use something like InVision's kind of web app. They've got a website kind of thing that you can use to add interactivity. Doesn't really matter which one you use. My favorite is Adobe XD. I've got a full course on that as well. So there's a 'UI and Web Design using Adobe XD' course. Go check that one out.