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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-.

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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

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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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HTML 

              
                <div class="note">You'll need a browser with support for <a href="http://caniuse.com/#feat=css-grid">CSS Grid</a> for anything below to look like much of anything notable.</div>

<ol>
  <li head on=1>User</li>
  <li head on=2>Page</li>
  <li head on=3>Service Worker</li>
  <li head on=4>Server</li>
  <li head on=5>Push Service</li>

  <li from=1 to=4>Navigation</li>
  <li back from=4 to=2>Page Load</li>
  <li from=2 to=3>register()</li>

  <li on=3>Register Push Handler</li>
  <li on=3>Register Notification Click Handler</li>
  <li back from=3 to=2>success</li>
  <li back from=2 to=1>Notification Permission Prompt</li>
  <li on=3>Worker is suspended</li>
  <li on=1>permission granted</li>
  <li from=1 to=2>success</li>
  <li on=2>endpoint and key generated</li>
  <li from=2 to=4>send endpoint & key</li>
  <li on=2>page blur or closed</li>
  <li break>*time passes*</li>
  <li on=4>event!</li>
  <li from=4 to=5>send message</li>
  <li back from=5 to=3>push event</li>
  <li on=3>worker is resumed</li>
  <li back from=3 to=1>display notification</li>
  <li on=1>click on notification</li>
  <li from=1 to=3>notificationclick event</li>
  <li back from=3 to=2>focus tab / open page</li>
</ol>
!

CSS 

              
                html {
  font-size: calc(1vw + .5rem);
}
body {
  font-family: sans-serif;
  margin: 1em;
}
.note {
  text-align: center;
  font-style: italic;
}
@supports (display:grid) {
  ol {
    padding: 0;
    display: grid;
    grid-template-columns: repeat(10, 1fr);
    list-style-type: none;
    background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='121' height='10'><rect x='60' y='0' width='1' height='10'/></svg>");
    background-size: calc(100% / 5) auto;
    background-position: top left;
    position: relative;
  }
  li {
    margin: 1em 0 1em;
    display: flex;
    align-items: center;
    text-align: center;
    justify-content: center;
  }
  li[on] {
    border: 1px solid black;
    background: #fff;
    margin: .3em 1em;
    padding: .25em .25em .1em .25em;
  }
  li[from] {
    background: linear-gradient(
      to top,
      #fff 0px,
      #000 0px,
      #000 .1em,
      #fff .1em
    );
    background-size: calc(100% - 8px) 100%;
    background-repeat: no-repeat;
    background-position: center top;
    padding: .3em 0 .4em;
    margin-left: 4px;
    margin-right: 4px; 
    position: relative;
  }
  li[from]:after {
    content: '';
    display: block;
    background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 10' ><path d='M5,0 L10,5 5,10z'/></svg>");
    background-repeat: no-repeat;
    width: .75em;
    height: .75em;
    position: absolute;
    bottom: 0;
    right: 0px;
    transform: translateY(calc(50% - .05em));
  }
  li[break] {
    grid-column: 1/11;
    margin: 1em 2em;
    background: #fff;
    padding: 1em 0;
    border-top: 1px dashed black;
    border-bottom: 1px dashed black;
    text-align: center;
  }
  li[back]:after {
    transform: translateY(calc(50% - .05em)) scale(-1,1);
    left: 0px;
  }
  
  [head] {
    grid-row: 1/1;
  }
  
  [from="1"] { grid-column-start: 2 }
  [to="1"] { grid-column-end: 2 }
  [on="1"] { grid-column: 1 / 3 } 

  [from="2"] { grid-column-start: 4 }
  [to="2"] { grid-column-end: 4 }
  [on="2"] { grid-column: 3 / 5 } 

  [from="3"] { grid-column-start: 6 }
  [to="3"] { grid-column-end: 6 }
  [on="3"] { grid-column: 5 / 7 } 

  [from="4"] { grid-column-start: 8 }
  [to="4"] { grid-column-end: 8 }
  [on="4"] { grid-column: 7 / 9 } 

  [from="5"] { grid-column-start: 10 }
  [to="5"] { grid-column-end: 10 }
  [on="5"] { grid-column: 9 / 11 } 
}
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JS
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