Then fill in a color of your choosing (like this red) the height you want. This example is 900 pixels high X 25 pixels wide for the whole file. The red part is 130 pixels high. Fill in the rest with another color. This example is with white.

Save as a .gif and put the file in your body tag as a background.
body background="file_name.gif"

Remember, putting an image in the body code with background= before it will make and an image tile and fill in the window. If this image had obvious edges, you would see the edges. Since it only has color, it tiles seamlessly.