title: change background color
body: <p>I am wondering why sometimes I can change the webpage background color and sometimes I can't. For example, in some sites I just type in document.body.bgColor = "red" in the chrome console, and the background color changed temporarily. However, in the other sites like StackOverFlow, this doesn't work. Since my browser has already loaded the page, I should be able to change how to displays it locally. Why not? Thank you  </p>