UI designers and web designers are not the same. A web designer is a person that designs content for the web. In some cases, a web designer is a graphic designer that works to build good looking apps or websites. A UI designer, on the other hand, is an individual that designs the entire screen which a user move and create the visual elements.
The user interface is created based on some functional requirement. A UI designer works with color, illustration, typography, visual design, photography, icons, and graphics. UI elements include icons, sliders, button, and scrollbars. Hope you find this information helpful.