Add animation to the background-image property in the body tag: step-by-step guide

Question

I am using background image in style tag.

<style>
body {
 background-image: url("img.jpg");
 background-size: cover;
 transition: background-image 4s linear;
 }
</style>

I want the image to fade in without adding a separate div to the page. Can this goal be achieved?

Answer 1

Yes, it is possible. You can do this.

@keyframes mymove {
     from {
      /* background: white; */     
     }
     to {
      background: url("https://www.shutterstock.com/image-photo/welded-metal-chain-various-rigging-260nw-2238426561.jpg");
       }
}
body {        
        animation: mymove 2s infinite;
      }

Answer 2

This is a CSS-only approach. However, there is a caveat, CSS cannot wait for events, so it has no way of knowing when the entire site has loaded.

Instead, in this snippet, it waits 1 second before starting to introduce the background image that is located on the body's before pseudo-element.

body {
  width: 100vw;
  height: 100vh;
  /*just for demo */
  position: relative;
}

body::before {
  background-image: url(https://picsum.photos/id/1015/1024/768);
  background-size: cover;
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: -1;
  opacity: 0;
  animation: fadein 5s 1 1s linear forwards;
}

@keyframes fadein {
  to {
    opacity: 1;
  }
}

Hello, this is some text in the body. It will be seen even before the background starts to fade in.