Fluent Design System CSS - improvement

I found this post: CSS-only Acrylic Material from Fluent Design System. It's great but it has a big problem: when I try to use more then one background-image it doesn't work anymore, because the following piece of code is needed:

body, .acrylic::before {
    background: url("img1.jpg") center/cover;
    background-attachment: fixed;
}

But I want to use different background-images for different page sections:

body {
    background: #FFF;     
}

.hero {
    background-image: url(img1.jpg);
}

.about {
    background-image: url(img2.jpg);
}

I need to be able to use the Acrylic effect anywhere on the page, like this:

<body>
  <div class="hero">
    <h1>I´m a hero</h1>
    <a href="#section">Scroll down link</a>
  </div>
  <div id="section" class="about"><p>Section has different background image <span class="acrylic">but this content is on the Acrylic Fluent Design surface<span/></p><div/>
</body>

So I need the Acrylic surface as a universal design component without the limitations of the original post. If somebody knows how to do it I will really appreciate any help.

Solution

The original answer to the question you link to states that:

Since we use same background for parent and children, we can club them together ;)

However this is not the case for your scenario, you actually want each element to have its own background, right? If I'm understanding you correctly, then you can remove this part of you css:

body, .acrylic::before {
  background: url("img1.jpg") center/cover;
  background-attachment: fixed;
}

Then to set the background for each section, plus the section's .acrylic background separately, see below:

main {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  width: 50%;
  float: left;
}

.acrylic {
  padding: 4em 6em;
  position: relative;
  overflow: hidden;
}

.acrylic::before {
  filter: blur(10px);
  content: "";
  position: absolute;
  left: -10px;
  top: -10px;
  width: calc(100% + 20px);
  height: calc(100% + 20px);
  z-index: -1;
}

.acrylic::after {
  content: "";
  position: absolute;
  left: 0;
  top: 0;
  right: 0;
  bottom: 0;
  z-index: -1;
  opacity: 0.35;
  border: 1px solid #fff;
  background: #fff;
  background-image: url(data:image/png;base64,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);
}

.shadow {
  border-radius: 1px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1), 0 1px 8px rgba(0, 0, 0, 0.2);
}

/* From here down are the changes to the original answer */

.hero,
.about {
  position: relative;
  z-index: -1;
}

.hero,
.hero .acrylic::before {
  background: url("https://images.unsplash.com/photo-1427434991195-f42379e2139d?auto=format&fit=crop&w=1189&q=60&ixid=dW5zcGxhc2guY29tOzs7Ozs%3D") center/cover;
}
    
.about,
.about .acrylic::before {
  background: url("https://images.unsplash.com/photo-1452723312111-3a7d0db0e024?w=700") center/cover;
}

<main class="hero">
  <div class="acrylic shadow">
    Acrylic material!
  </div>
</main>

<main class="about">
  <div class="acrylic shadow">
    Acrylic material!
  </div>
</main>