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HTML

              
                <main>
   <header class="inverted">
    <h2>demo of anchor(auto) and position-fallback</h2> 
     <p>When you scroll the image caption (initially at top) out of viewport, it should be rendered below the image</p>
  </header> 
 <section id="caption-auto-swap">
    <!-- nice, this can be anywhere in the markup --> 
    <figcaption>
      This image is generated by unsplash.it
    </figcaption>
    <h2>Implicit fallback positions with anchor(auto)</h2>
    <img src="https://unsplash.it/1280/720" class="responsive-image">
</section>
<section>
<p>
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Lorem mollis aliquam ut porttitor leo a diam sollicitudin. Ac placerat vestibulum lectus mauris ultrices eros. Lorem dolor sed viverra ipsum nunc aliquet bibendum. Convallis tellus id interdum velit laoreet id donec ultrices tincidunt. Vel elit scelerisque mauris pellentesque. Eget egestas purus viverra accumsan in. Tellus id interdum velit laoreet id. Elementum tempus egestas sed sed risus pretium quam vulputate dignissim. Bibendum enim facilisis gravida neque convallis a. Curabitur gravida arcu ac tortor dignissim. Risus commodo viverra maecenas accumsan. Tincidunt ornare massa eget egestas purus viverra.
</p>
  </section>

    <section id="caption-with-fallback">
<h2>Explicit fallback positions with position-fallback</h2>
      <figcaption anchor="hero-image-anchor">
    Another one by unsplash.it
</figcaption>
        <img id="hero-image-anchor" src="https://unsplash.it/1280/720" class="responsive-image">
    </section>
<section>
  <p>
Id aliquet lectus proin nibh nisl condimentum id venenatis a. Tempor orci dapibus ultrices in iaculis nunc. Vitae tempus quam pellentesque nec nam aliquam. Maecenas volutpat blandit aliquam etiam erat velit scelerisque in dictum. Aenean pharetra magna ac placerat vestibulum lectus mauris ultrices eros. Diam ut venenatis tellus in metus vulputate. Varius morbi enim nunc faucibus a. Auctor elit sed vulputate mi sit amet mauris commodo quis. Interdum velit laoreet id donec ultrices tincidunt arcu. Feugiat nisl pretium fusce id velit ut tortor pretium. Non blandit massa enim nec. Sem integer vitae justo eget magna. Nulla facilisi nullam vehicula ipsum. Lectus quam id leo in vitae. Sed enim ut sem viverra. Eu scelerisque felis imperdiet proin fermentum leo vel orci. Fermentum iaculis eu non diam phasellus vestibulum lorem sed risus. Accumsan tortor posuere ac ut. Ultrices neque ornare aenean euismod elementum nisi.
</p>
<p>
Id consectetur purus ut faucibus pulvinar elementum integer enim neque. Quam quisque id diam vel quam. Eget sit amet tellus cras adipiscing enim eu turpis egestas. Nibh nisl condimentum id venenatis a condimentum vitae sapien. Integer eget aliquet nibh praesent tristique magna sit amet purus. Aliquet risus feugiat in ante metus. Duis ut diam quam nulla porttitor. Amet porttitor eget dolor morbi non. Euismod elementum nisi quis eleifend quam adipiscing vitae proin sagittis. Amet massa vitae tortor condimentum lacinia quis vel eros. Faucibus purus in massa tempor nec feugiat. Sit amet massa vitae tortor. Urna id volutpat lacus laoreet non curabitur.
</p>
<p>
Pharetra convallis posuere morbi leo urna molestie. Suscipit adipiscing bibendum est ultricies integer quis auctor elit. In iaculis nunc sed augue lacus viverra. Vitae semper quis lectus nulla at volutpat. Non consectetur a erat nam at lectus. Viverra orci sagittis eu volutpat odio. Tempor commodo ullamcorper a lacus. Felis donec et odio pellentesque diam volutpat commodo. Turpis egestas pretium aenean pharetra magna ac placerat vestibulum lectus. Sagittis aliquam malesuada bibendum arcu vitae elementum. Quisque egestas diam in arcu cursus. Condimentum lacinia quis vel eros donec ac odio tempor. Arcu bibendum at varius vel pharetra. Eget arcu dictum varius duis at consectetur. Integer feugiat scelerisque varius morbi enim nunc faucibus a pellentesque. Ut eu sem integer vitae justo eget.
</p>
<p>
Amet porttitor eget dolor morbi non arcu risus quis varius. Enim sit amet venenatis urna cursus eget nunc scelerisque. Quis vel eros donec ac. Varius duis at consectetur lorem. Ut morbi tincidunt augue interdum. Fringilla ut morbi tincidunt augue interdum velit euismod. Nullam non nisi est sit amet facilisis. Sit amet nisl purus in mollis nunc sed id semper. Mauris rhoncus aenean vel elit scelerisque mauris pellentesque pulvinar. Curabitur vitae nunc sed velit dignissim sodales ut eu. Magna etiam tempor orci eu. Viverra adipiscing at in tellus integer feugiat. Tristique sollicitudin nibh sit amet commodo nulla facilisi. Nulla facilisi etiam dignissim diam quis enim lobortis scelerisque fermentum. Nulla pharetra diam sit amet nisl suscipit.
</p>
  </section>
</main>
              
            
!

CSS

              
                

#caption-auto-swap {
  margin-bottom: 2rem;
}

#caption-auto-swap img {
  anchor-name: --hero-image-1;
}

#caption-auto-swap figcaption {
  position: fixed; /* absolute does not work for some reason */
  /* works only with anchor-default for some reason */
  anchor-default: --hero-image-1;
/* 
  Align the fig caption’s bottom to the top of the anchor (hero image), but automatically swap if this overflows the window to the tooltip’s top aligns to the anchor’s bottom instead. 
  */
  bottom: anchor(auto);
  left: anchor(left);
  padding: .25em 0;
}

#caption-auto-swap figcaption::before {
  content: "⬛️";
  padding-right: .2em;
}

#caption-with-fallback img {
  anchor-name: --hero-image-fallback;
}

#caption-with-fallback {
  margin-bottom: 2rem;
}

#caption-with-fallback figcaption {
  position: fixed;
  anchor-default: --hero-image-fallback;
  position-fallback: --fallback1;
}

#caption-with-fallback figcaption::before {
  content: "⬛️";
  padding-right: .2em;
}

@position-fallback --fallback1 {
  @try {
    top: anchor(bottom);
    left: anchor(left);
    border: 2px solid black;
  }
  
  @try {
    bottom: anchor(top);
    left: anchor(left);
    border: 2px solid black;
  }
}


              
            
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JS

              
                
              
            
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