Icons and design

Most graphical environments (such as desktop, mobile, and more) have a default set of icons—those that are used to show file types, navigation arrows, and standard toolbars to help users recognize common actions. If your application is providing more than just the simplest of functionality, there will probably be a need to add some graphical elements to the design— most likely icons or symbols to help your users along. Will your additional icons match those provided by the environment the application is running in? If you are supporting just one platform, this is probably not an issue, but when you are aiming for a cross-platform solution, this could be much harder:

Windows uses a very different style to macOS

Think about this challenge when designing your application GUI: do you need additional icons or graphical elements?  Doing so may be different to the system style, but it may match your user's expectations.