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Learning to describe the bugs or issues you’re facing is a great skill to have in a developer, it may seem hard at first, but you should at least provide a brief summary of what you are trying to accomplish and what’s the error that shows up when you try to run your code.
It will also make it easier for others to help you if they know the problem beforehand.
In this particular problem, your supposed to replace the text inside of h1 element to “CatPhotoApp” so remove the “Hello world” and this should work just fine.
Whenever you’re stuck on a problem, your first reaction should be to look at the hints that show up when you try to run your code. Most of the time, you’ll find enough information in them to pass the challenge.