What Is The Title Of This Book? World Floods, And People Live On Floating Cities…?

I remember reading this book 5 years ago, problem is I can’t remember what it is called.
I remember it being based around this girl who used this globe thing to access what was probably the internet, the place she lived was being flooded by the rising sea levels and they managed to escape on a boat. They were told to head to this floating city where they would be accepted but they were kept outside in the harbour as refugees. The girl managed to escape using the disc things she’d found and she 1st uses the wrong one to get into the city.
people moved around the city on skates basically and slept in pods. She found someone who was head of the city using a strange implement that made marks on the paper (basically a pencil but that wasn’t stated in the book). I remember her finding the person she’d been speaking to online behind her in a particular room, and they both ended up underneath the city where there was trees etc and they, or one of them at least escaped to find actual land (i think)
I cant remember any more than that but I would really like to read this book again as I feel some of the issues raised in it would be really good to look at with some of my students.
If anyone can remember the title and author I would be very grateful.