I've started to create HTML websites, and I have a question about design. I want to get this efect in page borders, an efect like a shadow. But a shadow for all the page background between the content background and the background. I don't know how to do it and I want to learn. If someone could be so helpful I will be very plesant. Thanks. PD: excuse for my english, I'm from Spain. I hope you can understand me.

That effect is really not that hard to create.
In your graphic mock-up of the site (Photoshop or whatever you use), put the shadow on the section that will be your container or content background. The take a 'slice' of that background that INCLUDES the shadow on either side, it can be just a few pixels high so it should not be a big graphic.

Then you just add that 'slice' in as a background to the area you want to have the shadow on. That's what I did here: http://www.carolina-corvettes.com - the graphic is attached.

Thanks LadynRed, I will try what you say and if I have more questions I will return here.

Thank you again!