25% opacity. When you specify a background, you can set a background color, a background image, or both. If you set both, the browser displays the background color behind the image. As a result, you can only see the background color if the image has areas that are transparent, or the image doesn't repeat
50% opacity. If you add a background image to a box, it will repeat horizontally and vertically to fill the box by default. This works well for small images that are intended to be tiled across or down a box. If you want to change that behavior, you can set the background-repeat property.
75% opacity. By default, an image is positioned in the top left corner of the box. To change that, you use the background-position property. This property lets you specify both a horizontal and vertical position.