It is assembled from very affordable parts that can be pulled out of old Soviet technology or, like me, bought. All the details cost me 18 rubles. I used a smd resistor to reduce the bulkiness of soldering.
I used this circuit to illuminate the system unit with a LED strip with a 12v power supply, these same 12v I took from the fan connector on the motherboard. Enthusiasm for the capacitance of the capacitor can increase the time of "ignition" of the LEDs, you can also experiment with the nominal resistance.
Video with system operation: