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CSS

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JavaScript

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HTML 

              
                <p>Just setting the <code>--splash-bg</code> on <em>any</em> HTML element gives that element a background color, and a contrasting text color :)</p>
<span class="test" style="--splash-bg: 900"></span>
<span class="test" style="--splash-bg: 000"></span>
<span class="test" style="--splash-bg: 999"></span>
<span class="test" style="--splash-bg: 079"></span>

<h2>Resources:</h2>
<ul>
  <li><a href="https://www.todepond.com/lab/splash/" target="_blank">“Splash colour format”</a> by <a href="https://www.todepond.com/" target="_blank">Lu Wilson</a></li>
  <li><a href="https://lea.verou.me/blog/2024/contrast-color/" target="_blank">“On compliance vs readability: Generating text colors with CSS”</a> by <a href="https://lea.verou.me/" target="_blank">Lea Verou</a></li>
  <li><a href="https://kizu.dev/indirect-cyclic-conditions/" target="_blank">“Indirect Cyclic Conditions: Prototyping Parametrized CSS Mixins”</a> by <a href="https://kizu.dev/" target="_blank">Roma Komarov</a></li>
</ul>
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CSS 

              
                /* CSS Implementation of https://www.todepond.com/lab/splash/ */
/* A mixin prototype, see https://kizu.dev/indirect-cyclic-conditions/ for how this works */
@layer splash {
  * {
    /* Our input, with a list of “dependencies” */
    --splash-bg: var(--_splash-bg-value) var(--_splash-shadow) var(--_splash-color);

    /* Extracting the color components from the input */
    --_splash_r: round(down, var(--splash-bg) / 100, 1);
    --_splash_g: round(down, (var(--splash-bg) - var(--_splash_r) * 100) / 10, 1);
    --_splash_b: calc(var(--splash-bg) - var(--_splash_r) * 100 - var(--_splash_g) * 10);

    /* Normalizing the values to regular rgb: any changes and adjustements can go here */
    --_rgb_r: calc(var(--_splash_r) * 255/9);
    --_rgb_g: calc(var(--_splash_g) * 255/9);
    --_rgb_b: calc(var(--_splash_b) * 255/9);
    
    /* Assigning the actual value for the background color. */
    --_splash-bg-value: rgb(var(--_rgb_r), var(--_rgb_g), var(--_rgb_b));
    background: var(--_splash-bg-value, revert-layer);

    /* By default, adding a text-shadow (might be overridden later) */
    --_splash-shadow:
      Canvas 1px 1px 0px, Canvas -1px -1px 0px, Canvas 1px -1px 0px, Canvas -1px 1px 0px
      var(--WHEN, var(--_splash-bg-value));
    text-shadow: var(--_splash-shadow, revert-layer);

    /* If the browser supports relative colors, use them to assign a color instead of a shadow */
    /* See https://lea.verou.me/blog/2024/contrast-color/ for more details */
	  @supports (color: oklch(from red l c h)) {
		  --l: clamp(0, (l / var(--l-threshold, 0.71) - 1) * -infinity, 1);
      --_splash-color: oklch(from var(--_splash-bg-value) var(--l) 0 h) var(--WHEN, var(--splash-bg));
      color: var(--_splash-color, revert-layer);
      text-shadow: revert-layer;
    }
  }
}

:root {
  /* Required for indirect cyclic conditions */
  --WHEN: ;

  color-scheme: light dark;
}

.test {
  padding: 0.2em 0.4em;
  font: bold 1.3em/1.8 Helvetica, sans-serif;

  &::after {
    content: attr(style);
  }  
}

code {
  --splash-bg: 909;
}

em {
  --splash-bg: 099;
}
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JS
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