Design web and mobile app ui

My project is to design the user interface for a customer portal mobile and web app. The target audience that I have in mind is adults, so the design should be professional and appropriate for this age group. My preferred color scheme and design style is corporate and professional, and the type of app I need designed is a customer portal. Any design concepts should be suitable for adults and have an air of professionalism and sophistication. The app must also have intuitive navigability and be visually appealing.