Thanks for the reply! Actually I'm bad in English, Sorry for the inconvenience. By the way, This is what I wanted to know, see here in <img> tag, src image is "pic_bulboff.gif", only and this is normal that it refers to Turn off the light button. But where is the "pic_bulbon.gif" image source that can refer to Turn on the light button? What do you think, is it a magic or anything else that I don't know, Please?
Note: I'm going to practice with same codes in Notepad++ to make something like that and yes, I got a nice result without only an issue, that, there isn't any impact by clicking on Turn off the light and Turn on the light button. I saw, it is going to show me the result by depending on the source image (such as src="images/pic_bulboff.gif") between the buttons.
So, with same codes how is that possible there to turn on or turn off light in Tryit Editor ?
My result from notepad++ below...