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CSS

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <h1>
  I ❤ CSS
</h1>

<p data-bg="oddbird">
  please design responsibly…
</p>

<p style="--bg-hue: var(--mia-hue)">
  A pen by Miriam Suzanne
</p>
!

CSS 

              
                /* Generate a default background based on any hue */
body {
  --bg-hue: 270;
}

/* Override the default settings to customize your result */
h1 {
  --bg-hue: 180;
  --bg-tint-angle: to bottom left;
  --bg-tint-start: 70%;
  --bg-shade-angle: 80deg;
}

/* Create defaults that can be re-used via html */
[data-bg~='oddbird'] {
  --bg-color: hsl(195, 52%, 31%);
  --bg-tint: hsla(24, 100%, 62%, 0.75);
  --bg-shade: hsla(330, 100%, 45%, 0.75);
}


/* We could also provide preset values to choose from */
[style*='--bg-'] {
  --mia-hue: 330;
  --mia-color: hsl(330, 100%, 29%);
}


/* 
The mixin logic
---------------
- I've exposed more variables than you would need to.
  Each additional variable provides another "argument" to the API.
  For patterns that require less customization, use fewer variables.
- Defining it on the * selector makes this globally available,
  but it could also be scoped to any selector you want.
  Scoping functions/mixins to the DOM is a feature that only CSS can provide.
*/
* {
  /* Setting a valid hue (any unitless number) will auto-set all the other values */
  --bg-hue: unset;
  
  /* Adjust the base saturation and lightness as desired */
  --bg-saturation: 50%;
  --bg-lightness: 40%;
  
  /* set angles for the tint and shade gradients */
  --bg-tint-angle: -20deg;
  --bg-shade-angle: -110deg;

  /* set amounts for default tint & shade */
  --bg-tint-amount: 20%;
  --bg-shade-amount: 20%;
  
  /* set indiviidual hues for the tint and shade */
  /* defaults are set by higher-level arguments…
     which alows for both simpler & more customized uses*/
  --bg-tint-hue: var(--bg-hue);
  --bg-shade-hue: var(--bg-hue);
  
  /* set the gradient positions all at once */
  --bg-gradient-stops: 30%;
  
  /* override tint/shade gradients directly */
  --bg-tint-start: var(--bg-gradient-stops);
  --bg-tint-end: var(--bg-tint-start);
  --bg-shade-start: var(--bg-gradient-stops);
  --bg-shade-end: var(--bg-shade-start);

  /* override tint/shade saturation & lightness directly */
  --bg-tint-saturation: var(--bg-saturation);
  --bg-tint-lightness: calc(var(--bg-lightness) + var(--bg-tint-amount));
  --bg-shade-saturation: var(--bg-saturation);
  --bg-shade-lightness: calc(var(--bg-lightness) - var(--bg-shade-amount));

  /* or override any individual color directly */
  --bg-color: hsl(var(--bg-hue), var(--bg-saturation), var(--bg-lightness));
  --bg-tint: hsla(var(--bg-tint-hue), var(--bg-tint-saturation), var(--bg-tint-lightness), 0.25);
  --bg-shade: hsla(var(--bg-shade-hue), var(--bg-shade-saturation), var(--bg-shade-lightness), 0.25);

  
  /* this is the internal logic that creates your angled tint/shade background */
  --bg-image: 
    linear-gradient(
      var(--bg-tint-angle),
      var(--bg-tint) var(--bg-tint-start),
      transparent var(--bg-tint-end)
    ),
    linear-gradient(
      var(--bg-shade-angle),
      var(--bg-shade) var(--bg-shade-start),
      transparent var(--bg-shade-end)
    )
  ;
  
  /* Creating a final "output" variable acts like a function return */
  --bg: var(--bg-image) var(--bg-color);
  
  /* Applying that value to a property creates a mixin */
  /* Since the initial return is invalid, nothing happens unless we set a --bg-hue */
  background: var(--bg);
}


/* Just the layout */
* { box-sizing: border-box; }

body {
  display: grid;
  align-content: center;
  justify-content: center;
  grid-auto-rows: minmax(auto, 1fr);
  grid-auto-columns: minmax(auto, 1fr);
  grid-gap: 1em;
  min-height: 100vh;  
  padding: calc(2em + 10vmin);
}

h1, p {
  display: grid;
  align-content: center;
  justify-content: center;
  border: 2px solid white;
  margin: 0;
  padding: 1em;
}

p {
  color: white;
}
!

JS
!
999px

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