Hey dude, You need to replace the Hello World with CatPhotoApp text. For you information I would like to tell that you need to write every code between the <html> tag which has an opening <html> and a closing </html> tag. If sometimes you are unable to find solution try doing it from start in your initial journey of learning to code.
Hope this helps
Everything you want to put in an html file should be between <html> and </html>.
Everything related to the page’s body should be between <body> and </body>.
In your case, that <h1> in the last line should be above the </body>.