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HTML 

              
                <h1>Attempt at mixins, an example for the <a href="https://kizu.dev/layered-toggles/" target="_blank">layered toggles</a> article</h1>

<p>This example uses flex and grid layouts adapted from the <a href="https://smolcss.dev/" target="_blank">SmolCSS</a> project by <a href="https://thinkdobecreate.com/" target="_blank">Stephanie Eckles</a>.</p>

<p>Grid one works everywhere, where @layer is supported.</p>
<p>Flex one fully works only with style queries, as it requires styling the direct child (so only Chrome and Safari TP).</p>

<ol role="list">
  <li role="listitem">Item</li>
  <li role="listitem">Item</li>
  <li role="listitem">Item</li>
  <li role="listitem">Item</li>
</ol>

<ul role="list">
  <li role="listitem">Item</li>
  <li role="listitem">Item</li>
  <li role="listitem">Item</li>
  <li role="listitem">Item</li>
</ul>

<p>You can see how we can have <em>an element</em> with non-default display, and it not being affected by the mixins, even though they're defined with the universal selector, and involve adjusting the display property!</p>
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CSS 

              
                
:where(em) {
  display: inline-block;
  background: pink;
  padding: 0.25em;
  border-radius: 9em;
}

li {
  padding: 1em;
  box-sizing: border-box;
  background: var(--item-bg);
  border-radius: 1em;
  list-style-type: none;
}

ol,
ul {
  padding: 0;
  --min: 30ch;
}

ol {
  --layout: var(--smol-grid);
  --item-bg: lightgreen;
}

ul {
  --layout: var(--smol-flex);
  --item-bg: pink;
}

/* Due to layers, the display is not overridden even when having zero specificity. */

/* The mixins! */
* {
  /* Common variables. Ideally, we'd want to use `revert-layer` for them as well, but there is currently a number of issues with this: https://github.com/w3c/csswg-drafts/issues/9131 */
  @layer defaults {
    --min: 15ch;
    --gap: 1rem;
  }

  /* Layout mixins */
  /* Code adapted from https://smolcss.dev/ by Stephanie Eckles. */
  @layer {
    --layout: var(--no-layout);
    --no-layout: var(--layout,);
    --smol-grid: var(--layout,);
    --smol-flex: var(--layout,);

    display:
      var(--no-layout, revert-layer)
      var(--smol-grid, grid)
      var(--smol-flex, flex);
    gap:
      var(--no-layout, revert-layer)
      var(--smol-grid, var(--gap))
      var(--smol-flex, var(--gap));
    grid-template-columns:
      var(--no-layout, revert-layer)
      var(--smol-grid,
       repeat(
         auto-fit,
         minmax(
           min(100%, var(--min)),
           1fr
         )
       )
      )
      var(--smol-flex, revert-layer)
      ;
    flex-wrap: 
      var(--no-layout, revert-layer)
      var(--smol-grid, revert-layer)
      var(--smol-flex, wrap)
      ;
    @container not style(--smol-flex: ) {
      /* Otherwise, it will be reset on `*` */
      --min: inherit;
      flex: 1 1 var(--min);
    }
    
  }
  
}
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