How to Stretch a Background Image to Fit a Web Page

Images are an important part of attractive website designs. This includes the use of background images. These are the images and graphics that are used behind areas of a page as opposed to images that are presented as part of the content pages. These background images can add visual interest to a page and help you achieve the visual design that you may be looking for on a page.

If you begin working with background images, you will undoubtedly run into the scenario where you want an image to stretch to fit the page. This is especially true for responsive websites that are being delivered to a wide range of devices and screen sizes.

This desire to stretch a background image is a very common desire for web designers because not every image fits in the space of a website. Instead of setting a fixed size, stretching the image allows it to flex to fit the page no matter how wide or narrow the browser window is.

The best way to stretch an image to fit the background of an element is to use the CSS3 property, for background-size, and set it equal to cover.

div {
 background-image: url('background.jpg');
 background-size: cover;
 background-repeat: no-repeat;
}

Take a look at this example of it in action. Here's the HTML in the image below.

Now, take a look at the CSS. It's not much different than the code above. There are a few additions to make it clearer.

Now, this is the result in full screen.

By setting background-size to cover, you'll guarantee that browsers will automatically scale the background image, however large, to cover the entire area of the HTML element that it's being applied to. Take a look at a narrower window.

According to caniuse.com, this one is supported by over ninety percent of browsers, making it an obvious choice in most situations. It does create some problems with Microsoft browsers, so a fallback might be necessary.

Here is an example that uses a background image for the body of a page and which sets the size to 100% so that it will always stretch to fit the screen. This method isn't perfect, and it might cause some uncovered space, but by using the background-position property, you should be able to eliminate the problem and still accommodate older browsers.

body {
 background: url('bgimage.jpg');
 background-repeat: no-repeat;
 background-size: 100%;
 background-position: center;
} 

Using the example from above with the background-size set to 100% instead, you can see that the CSS looks mostly the same.

The result on a full screen browser, or one with similar dimensions to the image is nearly identical. However, with a narrower screen, the flaws start to show.

Clearly, it isn't ideal, but it will work as a fallback.

According to caniuse.com, this property works in IE 9+, Firefox 4+, Opera 10.5+, Safari 5+, Chrome 10.5+, and on all the major mobile browsers. This covers you for all the modern browsers available today, which means you should use this property without fear that it will not work on someone's screen. 

Between these two methods, you shouldn't have any difficulty supporting nearly all browsers. As background-size: cover gains even more acceptance among browsers, even this fallback will become unnecessary. Clearly, CSS3 and more responsive design practices have simplified and streamlined using images as adaptive backgrounds within HTML elements.