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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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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. For instance, CoffeeScript can help prevent easy-to-make mistakes and offer a cleaner syntax and Babel can bring ECMAScript 6 features to browsers that only support ECMAScript 5.

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Babel is required to process package imports. If you need a different preprocessor remove all packages first.

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About External Resources

You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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HTML 

              
                <button id='show' onClick='showDialog()'>Show Dialog</button>
<div id='text'>
  <p>It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, we had everything before us, we had nothing before us, we were all going direct to Heaven, we were all going direct the other way-- in short, the period was so far like the present period, that some of its noisiest authorities insisted on its being received, for good or for evil, in the superlative degree of comparison only.</p>

<p>There were a king with a large jaw and a queen with a plain face, on the throne of England; there were a king with a large jaw and a queen with a fair face, on the throne of France. In both countries it was clearer than crystal to the lords of the State preserves of loaves and fishes, that things in general were settled for ever.</p>

<p>It was the year of Our Lord one thousand seven hundred and seventy-five. Spiritual revelations were conceded to England at that favoured period, as at this. Mrs. Southcott had recently attained her five-and-twentieth blessed birthday, of whom a prophetic private in the Life Guards had heralded the sublime appearance by announcing that arrangements were made for the swallowing up of London and Westminster. Even the Cock-lane ghost had been laid only a round dozen of years, after rapping out its messages, as the spirits of this very year last past (supernaturally deficient in originality) rapped out theirs. Mere messages in the earthly order of events had lately come to the English Crown and People, from a congress of British subjects in America: which, strange to relate, have proved more important to the human race than any communications yet received through any of the chickens of the Cock-lane brood.</p>
</div>
<div id='dialog'>
  <span>Oh wow, modal! We can close this now.</span>
  <button id='close' onClick='closeDialog()'>Close Dialog</button>
</div>
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CSS 

              
                body {
  font-size: 1.5em;
  justify-content: center;
  line-height: 1.5;
  margin: 0;
  padding: 1em 3em;
}
#text {
  max-width: 800px;
}
#dialog {
  display: none;
  position: fixed;
  top: 10vh;
  left: 10vw;
  width: 80vw;
  height: 80vw;
  border: 1px solid #eee;
  border-radius: 4px;
  padding: 10px;
  text-align: center;
  z-index: 1;
  background-color: #444;
  color: #fff;
}
#dialog.show {
  align-items: center;
  display: flex;
  flex-direction: column;
}
#dialog span {
  margin-bottom: 1em;
}
#show,
#close {
  background: #da1b60;
  border: none;
  color: #fff;
  display: block;
  font-size: 1em;
  padding: 1em;
  width: 200px;
}
#show:hover,
#close:hover {
  background: #ff8a00;
  cursor: pointer;
}
#show {
  position: fixed;
  top: 30px;
  left: 10px;
}
#close {
  position: relative;
}
!

JS 

              
                const showDialog = () => {
  document.getElementById('dialog').classList.add('show')
  const scrollY = document.documentElement.style.getPropertyValue('--scroll-y');
  const body = document.body;
  body.style.height = '100vh';
  body.style.overflowY = 'hidden';
};
const closeDialog = () => {
  const body = document.body;
  const scrollY = body.style.top;
  body.style.position = '';
  body.style.top = '';
  body.style.height = '';
  body.style.overflowY = '';
  window.scrollTo(0, parseInt(scrollY || '0') * -1);
  document.getElementById('dialog').classList.remove('show');
}
window.addEventListener('scroll', () => {
  document.documentElement.style.setProperty('--scroll-y', `${window.scrollY}px`);
});
!
999px

Console