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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Adding Classes

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About the <head>

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <figure>
  <div class="outer">
    <div class="inner">
    </div>
  </div>
  <figcaption>
    <span class="outer-radius">50</span>px 
    - 
    <span class="padding">25</span>px 
    = 
    <span class="inner-radius">25</span>px
  </figcaption>
</figure>

<form>
  <label>
    Outer Border Radius
    <input type="range" min="0" max="100" value="50" name="radius"/>
  </label>
  
  <label>
    Gap
    <input type="range" min="0" max="50" value="25" name="padding"/>
  </label>
</form>
!

CSS 

              
                :root {
  --demo-width: min(20em, 80vw);
  --hue: 220;
  --stroke-hue: 275;
}
figure {
  --padding: 25px;
  --radius: 50px;
  
  --demo-width: min(20em, 80vw);
}

* {
  margin: 0;
}

html, body {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100%;
  font-family: Source Sans Pro, Source Sans, system-ui, sans-serif;
}

body {
  padding-block: 1em;
  gap: 2em;
  background-color: hsl(var(--stroke-hue), 20%, 90%);
}

figure {
  background: hsl(var(--stroke-hue), 60%, 98.5%);
  box-shadow:   0px 0.8px 2.2px hsla(var(--hue), 100%, 10%, 0.02),
  0px 1.9px 5.3px hsla(var(--hue), 100%, 10%, 0.028),
  0px 3.6px 10px hsla(var(--hue), 100%, 10%, 0.035),
  0px 6.5px 17.9px hsla(var(--hue), 100%, 10%, 0.042),
  0px 12.1px 33.4px hsla(var(--hue), 100%, 10%, 0.05),
  0px 29px 80px hsla(var(--hue), 100%, 10%, 0.07);
    
  width: var(--demo-width);
  height: var(--demo-width);
  padding-top: 1em;
  padding-left: 1em;
  display: grid;
  place-items: stretch;
  position: relative;
}

figcaption {
  background: hsl(var(--hue), 60%, 95%);
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  padding: 0.5em;
  text-align: center;
  font-variant-numeric: tabular;
  font-size: 1.5em;
}

.outer { 
  background: hsl(275, 95%, 60%);
  display: grid;
  place-items: stretch;
  padding-top: var(--padding);
  padding-left: var(--padding);
  border-top-left-radius: var(--radius);
}

.inner {
  background: hsl(220, 30%, 85%);
  border-top-left-radius: calc(var(--radius) - var(--padding));
}

form {
  width: var(--demo-width);
  display: grid;
  gap: 1em;
}

label {
  font-weight: bold;
  font-size: 1.25rem;
}

input {
  accent-color: hsl(275, 95%, 60%);
  display: block;
  width: 100%;
}
!

JS 

              
                const figureEl = document.querySelector('figure');
const inputs = document.querySelectorAll('input');

const radiusInputEl = document.querySelector('[name="radius"]');
const paddingInputEl = document.querySelector('[name="padding"]');

const outerRadiusEl = document.querySelector('.outer-radius');
const innerRadiusEl = document.querySelector('.inner-radius');
const paddingEl = document.querySelector('.padding');

function updateFigure({target}) {
  figureEl.style.setProperty(`--${target.name}`, `${target.value}px`);
    
  outerRadiusEl.textContent = radiusInputEl.value;
  paddingEl.textContent = paddingInputEl.value;
  innerRadiusEl.textContent = radiusInputEl.value - paddingInputEl.value;
}

document.addEventListener('input', updateFigure);
document.addEventListener('change', updateFigure)
!
999px

Console