Light dimmer not working
Online circuits aren't always good circuits to start with, they are sometimes tuned to the exact parts that were used without an analysis that proves that the circuit will work with normal part variations.
The 200 ohm should be smaller, probably 120 ohms. But this isn't your main issue. This will limit the minimum phase angle, but the large triac would still fire for larger angles.
The problem is in the zero-cross detector, you should increase the current in the opto diode, I would use 27k instead of 47k. If you go lower than that, you will need a higher wattage resistor. Power with 27k will be 120^2/(27k*2), shared with 2 resistors. 1/4W de-rated 50% is good, assuming that your circuit is operated at normal temperatures.
The circuit may still be marginal, the emitter resistor is rather small. I would increase the 1k to 4.7k. To be sure, you should analyze the current transfer ratio using the exact part that you have used. There are a lot of options for the EL817, I don't know which variation that you have used.