1. Open the Story Project in the Twine 2 application.
note: If you don't have access to the original project then you can recreate it by using the applications Import From File option to import the story HTML file.
2. Create a new Passage, you can name it whatever makes sense to you, and then assign a header tag to the new passage.
3. Cut-and-paste your code example into the new header tagged Passage.
During the running of the story you will notice that the contents of the header section will appear instantly while the displaying of the contents of the current passage will fade in. The instant displaying of the header content is a result of you using HTML elements within a Passage (any type of Passage) combined with how Harlowe performs the passage fade-in.
I don't know of a way around this effect but a more experienced CSS writer may.