I’m not sure if I’d classify the story as full on dark, because there are some light hearted aspects in there. Sometimes it can be very dark when something serious happens, but it never stays that way for too long. Its kind of like real life, you have your really good days and you have your really bad days. I just want to know what genres would suit that kind of story.
As was already pointed out in a comment, I am pretty sure that works in most genres. Two things I would keep in mind:
Watch genre expectations: e.g. in Romance especially (where a good ending is kind of expected I've heard) or Children's, as well as YA if you overdo it, this might be a problem.
Integrate it into the marketing: it might not be wise to have a cute cover and purely positive teaser text, since in general people like to be surprised by plot twists but not by overall content and tone, at least not too much. Inside the story itself, hinting at the upcoming escalation at various points with foreshadowing may also help. Otherwise, you may lose readers who wouldn't read purely for the happy part but are willing to stick with it for the darker things.