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    All paragraphs have <code>--warning</code> set to
    so it has a pink background
    and border.
    <em>The mixin has been mixed in!</em>
    We can turn off both the background and border 
    by changing the value of <code>--warning</code>
    on the <code>last-child</code>.
      The previously-mixed-in mixin 
      has been <strong>un-mixed</strong>
      in a single declaration!

  This 'mixin' technique was described by Roma Komarov in
  <a href="">Layered Toggles: Optional CSS Mixins</a>.


                @layer reset, base, mixins;

p {
  --warning: var(--warning--on);

p:last-child {
  --warning: var(--warning--off);

/* Define mixins in the highest layer */
@layer mixins {
  *:not(:focus):not(:active) {
    --warning: var(--warning--off);
    --warning--off: var(--warning,);
    --warning--on: var(--warning,);

      var(--warning--off, revert-layer)
      var(--warning--on, pink);
      var(--warning--off, revert-layer)
      var(--warning--on, thick solid deeppink);
      var(--warning--off, revert-layer)
      var(--warning--on, 1em);

@layer base {
  body {    
    --text-small: clamp(0.938rem, 0.824rem + 0.568cqi, 1.25rem);
    --text-normal: clamp(1.25rem, 1.023rem + 1.136cqi, 1.875rem);
    --text-large: clamp(1.35rem, 0.818rem + 2.659cqi, 2.813rem);
    --text-xlarge: clamp(1.7rem, 0.784rem + 4.58cqi, 4.219rem);
    --gap: clamp(12px, 0rem + 3.75cqi, 24px);
    font-size: var(--text-normal);
    padding: var(--gap);
  footer {
    border-block-start: thin dotted;
    padding-block-start: 1em;

@layer reset {
  * { box-sizing: border-box; }
  html { block-size: 100%; }
  body {
    margin: unset;
    min-block-size: 100%;
  svg {
    display: block;
    max-inline-size: 100%;
  picture { display: contents; }
  select {
    font: inherit;