Some important things to know:
The red wire and the reference to positive and negative are clues that either there is something else going on or this is non-standard junk. As it turns out, there is something else going on. The installation page is available for download from the product page.
There is an LED driver as a separate component together with this light fixture. Many other light fixtures include the driver as a part of the light fixture. There are some advantages to a separate LED driver:
- Replaceable if it fails
- Low voltage wiring is used to connect the driver to the light fixture, which relaxed rules compared to 120V AC wiring.
- One driver can, depending on design and installation, be used to power multiple light fixtures
But it is different from the usual setup. Hopefully you didn't kill the light fixture by connecting 120V AC to a device designed for low voltage DC. The dimmer switch may have been damaged as well.
The LED driver is connected to the hot (black in your case) and neutral (white) wires. The light fixture itself has red and black wires which connect to the LED driver. Polarity is meaningless for AC, but matters for DC.
There are two ways to install this. One is to attach the driver to the existing ceiling box. There may or may not be space to do so properly. If you do that, the driver attaches to black and white, the light fixture red and black wires attach to the driver and you're done. It may be worth testing this before going any farther, because this will tell you whether the fixture is still functional or not, even if you can't actually complete the installation in this location.
The second method, which is what the instructions recommend, is to install the driver at a "remote and accessible location near the fixture". This could be in a box next to the switch or in some intermediate location. But it needs to be accessible, meaning nothing beyond a screwdriver to get to it for repair or replacement. You run regular (black/white) cable from the switch to the driver. You run a separate from 120V AC cable from the driver to the ceiling box, where it will connect with the fixture. If you use regular (black/white) 2 wire cable, put red tape on each end of the white wire to indicate it is not neutral.
Separate is a key word here. In a typical home, a light fixture ceiling box might include switched hot and neutral to a fixture but also hot coming in from elsewhere and going out to elsewhere and neutral from/to elsewhere with all the white neutral wires connected. That won't work here, because:
- Low voltage and 120V/240V wires can't be in the same box (that's a strict code rule)
- Even if they could be in the same box, this white wire is not neutral and must not be connected to neutral wires (which is a good reason to not have them in the same box even if it wasn't a strict code rule)
To be honest, it may be a lot easier to simply get a fixture that has an integral driver.