Up until mid-2019, Earth looked exactly as you would expect it to. But in the middle of June, all across the planet people heard and felt an earth-shaking BANG, signalling the reappearance of something long-dormant:

Magic had returned to Earth.

Urban Fantasy

Some time around the roman empire, magic faded.
Nobody is quite sure what happened, as nobody except the most magically inclined noticed it was happening at the time: sorcerers found magic infinitely harder to use; several liches suddenly disappeared as their phylacteries were unable to sustain their bodies, and went inactive to preserve the souls inside; the dragons disappeared one by one, finding themselves unable to stay awake; many other magical creatures vanished or became nonmagical.
There was still magic around, but only the tiniest smidgen compared to how it had once been, and as the years passed, anyone who tried to practice magic assumed that the strength that it was at was how it always had been.
Then, in the middle of June, the year 2019, a loud bang was heard around the world. Sleeping people were startled awake, deaf people felt the world shake around them, and the next day people everywhere found themselves witness to impossible things.

True physics work exactly the way the way we know them, but when magic gets involved things get somewhat wonky. Gravity can be circumvented, atoms can rearrange themselves, the only thing that seems truly constant is the laws of motion.

Magic depends entirely on belief. The way you think magic works, and how it should behave, is how it behaves for you. This means that magic is only as complicated as you think it should be: some people may need to draw complex spell-circles to do magic, or act out a many-parted ritual, while some may simply need to concentrate and twist their hands just so.
It has its limits, but nobody quite knows what they are, except that Magic Itself seems to have a sense of humour and likes proving people wrong