Customizing classic green bits

[gjh42]

#someId
{
  background-image: url(../images/yourimage.gif); //use relative file path
  background-position: top left; //(top/center/bottom left/center/right) or (x-% y-%) or (x-pos y-pos)
  background-repeat: repeat-x; //or repeat or repeat-y or no-repeat
  background-attachment: scroll; //or fixed
} 

Look at w3schools.com for comprehensive tutorials on this and other subjects, and interactive demos to get a feel for using the declarations.