The Cover
The cover is mostly just css, there are some things you can do with it and an intersection observer, but reread the book chapter if that sounds like something you are interested in.
header content
whatever content
Use minHeight to specify the height of this container. Default is 100dvh
header content
whatever content
This one is 50dvh and has style="text-align: center;" to center the
text in it horizontally and center-flex class to center it vertically.