To remember which way the cathode (negative) end is on a surface-mount LED, look at the green thing on the underside. It’s a tree, sticking into the ground. It looks like a ground symbol on a schematic. The ground end is ground. There you go.
For some reason, SMD/SMT LEDs sometimes have a green stripe on the top. Sometimes it’s on the anode side, sometimes it’s on the cathode. As far as I can tell, it’s random.