Changes in style.css do not take place.

Ow boy,

I’m working with CSS for one week now and things go pretty well. Till today. The changes I make in the css-code in the editor, will not change my website. Even simple changes as changing the color of the background. It seems that the css code will not update.

Usually I copy my whole style.css code in a Dreamweaver-file (which I use as backup). And then copy this back into the editor. I use the Twenty Twelve team.

But nothing seems to change anymore. What could have go wrong?