Blinking 2 LEDs at random interval

Hai, which code can I use to blink 2 LEDs at random interval simultaneously? I use the code below, but it seems like both led will light up at the same time. And also my blue led only turn off after red led to turn off

delay(random(1000, 4000));
    digitalWrite (LED_blue, HIGH);
    digitalWrite (LED_red, HIGH);
    delay(random(1000, 10000));

    digitalWrite (LED_red, LOW);
    delay(random(1000, 8000));

    digitalWrite (LED_blue, LOW);
    delay(random(1000, 8000));

Take a look at this guide.

Take a look at Using millis() for timing. A beginners guide, Several things at the same time and the BlinkWithoutDelay example in the IDE