Fullscreen websites are those that fill the entire browser window no matter what the screen resolution is. As screen sizes and resolutions are growing and internet speed is increasing, it seems like more and more web designers use full screen images for their websites backgrounds. Oversized background images can be stunning and have more visual impact than the traditional tiled background graphics.
The browser viewport is a fluid medium. There are many options to produce full screen backgrounds and ways to place HTML over the images. Some websites depend on a flexible layout to stretch across the browser window, while others use large images with a fixed size to produce large backgrounds. But the easiest way to stretch any background image in a browser window is to use a background image in CSS.