How Can I Make Background Images Responsive Using CSS?

Achieving Responsive Background Images with CSS

In web design, it's often desirable to have background images that adapt dynamically to different screen sizes. To achieve this, you want the image's width to fit the available space, while preserving its aspect ratio and scaling the height proportionally.

Using background-size: cover;

To accomplish this, CSS3 offers the background-size property. Specifically, setting it to cover ensures that the background image scales to fill the entire available space, maintaining its proportions. The image will be cropped vertically if necessary to fit, allowing for vertical scrolling without horizontal repetition.

Here's an example code that demonstrates this:

body {
    background-image: url(images/background.svg);
    background-size: cover;
    background-repeat: no-repeat;
    background-position: center center;
}

How Contain and Cover Differ

Contain: Scales the image to fit entirely within the background positioning area while preserving its aspect ratio. This may result in empty spaces around the image.

Cover: Scales the image to cover the entire background positioning area while maintaining its aspect ratio. This may result in cropping the image to fit.

Understanding the Visual Impact

Consider an image with a resolution of 4x3 being used as a background for a 16x9 screen.

Contain: The image fits within the screen but leaves empty space on either side.

Cover: The image covers the entire screen but cuts off a portion at the top and bottom.

To illustrate this difference, here's a demonstration:

<div class="contain">
    <!-- Background image will fit, leaving empty space -->
</div>
<div class="cover">
    <!-- Background image will cover, cropping as needed -->
</div>

.contain, .cover {
    width: 20em;
    height: 10em;
    background-image: url(example.jpg);
    background-repeat: no-repeat;
    background-position: center center;
    background-color: #ccc;
    border: 1px solid;
}

.contain {
    background-size: contain;
}

.cover {
    background-size: cover;
}

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