If it's possible, can you send me a schema of the circuit ?
Connect one side of the switch to a digital pin. Connect the other side to ground. Enable the internal pullup resistor. Hard to get much simpler than that,
After the pinMode() statement, for the switch pin, add
digitalWrite(bouton, HIGH); // Enable the pullup resistor.
My problem is, when I push on the button, ALL the leds (ON too) switch off ... I don't know why ...
Your problem is likely that the pin is floating, because you do not have a pullup or pulldown resistor.
Or, I don''t understand, because you only have one LED defined/used. So, the difference between one and all escapes me.