To make the picture full of the screen as the background, the key is to use background-size: cover and combine positioning settings. The specific steps are as follows: 1. Set margin: 0 and min-height: 100vh for the body; 2. Use the background attribute to specify the image path and set it to center fixed; 3. Add background-size: cover to maintain scale filling of the viewport; 4. If you need to overlay multiple pictures, use multiple backgrounds and arrange them in the stacking order; 5. Pay attention to optimizing the image format, adapting to focus areas, and handling cross-domain issues to ensure performance and compatibility.

If you want a picture to fill the entire screen as the background, using CSS is actually quite simple, but there are several key points to pay attention to. The most common method is to combine background-size: cover with some positioning settings, which ensures that the image always covers the entire viewport while maintaining proportions.

Set the basic structure of a full-screen background

First, you need an HTML element to host the background image, which is usually done directly on :

 body {
  margin: 0;
  min-height: 100vh;
  background: url('your-image.jpg') no-repeat center center fixed;
  background-size: cover;
}

After setting this way, the picture will automatically scale according to the browser window and will be displayed in a center, without leaving blank or deformed. Be careful to clear margin , otherwise the default margin may affect the effect.

If you want the background image to be fixed (for example, the image to be fixed when scrolling the page), you can add background-attachment: fixed , but this attribute may not take effect on the mobile side and additional processing is required.

Overlaying techniques for multiple background images

Sometimes you may not just want a picture, such as adding a gradient mask or multiple levels of background. You can use multiple backgrounds at this time:

 body {
  background-image: url('overlay.png'), url('background.jpg');
  background-position: center center, center center;
  background-repeat: no-repeat, no-repeat;
  background-size: cover, cover;
}

This method is suitable for some visual effects, such as adding a translucent mask layer to cover the background image to improve the readability of the text. Note that the order is from front to back, and the first picture is at the top level.

Pay attention to adaptation and performance issues

Although cover is very useful, there are some potential problems that need to be paid attention to:

• The image is too large and slowly loading. It is recommended to compress and use a suitable format (such as WebP)
• Some parts on the small screen may be cropped, choose the focus area
• If the image comes from an external link, consider cross-domain issues (especially when using canvas or video backgrounds)

If you find that the background image flashes when the page is loaded, you can consider preloading the image or use opacity to fade into the transition.

Basically that's it. Use background-size: cover and coordinate with positioning and hierarchical control to create a stable and beautiful full-screen background image.

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