How to make CSS (or JS?) hideable help bar

Sort of how this website shows a bar on top when you have new answers or comments, I want to show a very similar bar that j开发者_如何学JAVAust has a line of text in it and an [X] to close it. How would I begin to do this?

Here is how you can create it :)

You can simply keep a div with the position of your wish and use CSS for hiding the same. Whenever you need to show something, set the text inside and set the CSS to show the same. Upon clicking the [X], the CSS can be reset.