Sky-sama

It doesn't resize the image at all .How to resize using css?

I have been working for hours, but I don't really know how to make my header fit the browser width.I'm using a big image as header (1920x1080), but I don't know how to fit the browser window. I'd like to make something that looks like this:http://i53.tinypic.com/21nffr8.pngCould you please help me?Your support is appreciated .