The phone likely charged fully to 100%. There are several features that protect the battery health and prolong its lifespan. One of those stops the device from constantly charging when plugged in overnight. Just plug it back into a charger and keep an eye on it to confirm that it reaches 100%.
Mine did the same but on the screen said it was protecting my battery. It stops charging at 100% in order to keep it from overheating. Unplug it and plug back in to get back to 100%
