Light switch installation
The red is your switched-hot, so connect the black from your fixture to that
It appears that your switch was wired so that always-hot could be passed along to downstream lighting outlets while providing a switched-hot at those outlets as well, while power comes in at the switch.  So, you need to turn the breaker off and move the black wire from the fixture over to connect with the red wire from the ceiling instead of the black wires.  Then you can button the fixture back up, turn the breaker back on, and enjoy your new switch!