Check a checkbox after loading page

I try to learn CSS by making a website I fond on internet a code to display text on a Facebook chat style. I just don't know how to make it always open when I open the page. I tried to change the values of content of it don't seems to work...

Here is the link : http://js http://ift.tt/1KiNuD8

Sorry or my bad English, and thx for the responses !