Layers Help

This seems like the simplest thing, but I am making a hard time of it.

I am trying to build my page layout using layers and CSS. I would like some of my layers to start about 100px from the left hand side and extend across the page until about 10px from the right. So when the browser window is rescaled the layer will still start 100px from the left but will expand so it ends 10px from the right.

Could someone show me some generic html and css script that would acomplish this.

Thanks.

_t