Lit Formation Flying Fast Horizontally

While watering in my backyard in Elysian Heights I looked absentmindedly up to the sky and suddenly saw a formation of 2-3 bright lights streaking across the sky in the direction of Hollywood. I would say they were traveling northwest.
Although the formation entered from outside my field of vision, I was able to view them for some time crossing my field of vision. There was a bright blue one, what seemed like a light green, and then a red one, that looked rather like a plane light. All three of these lights were stacked very nearby one another, and moving together. I assumed it was a plane and then a firework, but I noticed no sound emitted whatsoever, during or at the end.
I only realized it could not have been a plane nor a firework once it was gone. Firstly, the formation was moving horizontally across the sky at a low altitude. Secondly, the lights moved together in a line and then seemed to separate and then “fizzle out” before leaving my field of vision. Due to this I thought it could be a firework… But a firework lit on the ground would not have the chance to travel so far horizontally, and at such great altitude. It would also have made some noise —this was silent.
I was on a hill near the highest point, and the lights were far above the crest of the mountains. You couldn’t shoot a firework off from that height.
A drone, too, would not have been able to travel that fast, perhaps unless it was a stealth military unmanned drone…but the multiple lights and the splitting up of the formation looked to me like it was multiple objects OR that one object was breaking up, the way something would in the atmosphere. However it was not moving down, but sideways.
This made me think of a shooting star as well. But a shooting star appears to happen much higher up in the atmosphere, and fizzle out as it approaches the Earth.
These were definitely moving HORIZONTALLY across the sky, not vertically up or down.
From my perspective, the phenomenon occurred right above Sunset Blvd on the way from Echo Park to Silverlake, so I assume that other people will have noticed it too. This is a densely populated area and the sighting occurred in a fairly visible place. They left no trail, other than maybe a light trail on my retinas. The whole thing must have lasted only a few seconds, the way a firework does as you watch it burn and fizzle out.
I only caught the end of this event. It was clear to me that the objects had already been moving for a considerable amount of distance/time by the time I saw them. This i judge by the speed at which they moved once I noticed them.
Overall a very curious event that I will be wondering about for a long time.