Complexity invites bugs. Less complex your requirement, less bugs.
For example, showing button on HTML page may not generate the bugs. But the button that triggers specific notification for say mobile and web in a different context at the same time releasing the data to database. And having additional activity dependent on such button click may invite bugs on different platforms and even on the server side.
In short your project complexity decides how many bugs can be generated and how many of them can be fixed. Also there is no such thing as bug free software. You can write bug free software for specific modern machines but people on legacy machines may have issue and so on.