You can also apply background to body element instead of html. because all of the visible content is inside in the body tag.How do I combine a background-image and CSS3 gradient on the same element? CSS opacity only to background color not the text on it? Today we will create a CSS-only fullscreen background image slideshow. Opacity: 0.4 VS 2012 W/VB.net code behind Semi transparent background image body background-image: You should have specified it to be CSS. I havent been able to find a a method in CSS that would allow you to change the opacity of a background image (without just having it as a DIV behind the DIV youre actually working with), but I know of two other methods you could try!