[SOLVED] Why don't CSS blend modes work when applied against the document body?

Why don't CSS blend modes work when applied against the document body?

Here's an example of CSS blend modes working against a specified "background" element:

body {
  position: relative;
}

.background {
  position: absolute;
  top: 0; left: 0;
  height: 100%;
  width: 100%;
  background: linear-gradient(red, blue);
}

.blend {
  background: green;
  mix-blend-mode: difference;
}

<body>
  <div class="background"></div>
  <div class="blend">BLEND ME</div>
</body>

And here's an example of the blend mode not applying over the body:

body {
  background-image: linear-gradient(red, blue);
  background-size: 100%;
  background-repeat: no-repeat;
}

.blend {
  background: green;
  mix-blend-mode: difference;
}

<body>
  <div class="blend">BLEND ME</div>
</body>

What gives? Is the body element not considered when calculating CSS blend modes? Does this apply in all browsers? Who am I and why am I here? This came up as an issue when attempting to implement dynamic (via scroll) blending over a body with background-attachment: fixed.

UPDATE: This appears to only apply in Chrome; Firefox/Safari behave expectedly - what's up with Chrome?

Solution

The body element does blend in Chrome, but only if its background isn't propagated to the canvas.

To stop it doing that, add a background for the <html> element.

html {
  background-color: white;
}
body {
  background-image: linear-gradient(red, blue);
  background-size: 100%;
  background-repeat: no-repeat;
}
.blend {
  background: green;
  mix-blend-mode: difference;
}

<body>
  <div class="blend">BLEND ME</div>
</body>