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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

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 Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import usage.

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HTML 

              
                // by twitter.com/dbox

body.debug
  section
    article      
      hgroup
        h1 debug()
        
      p  Toggle this on a parent element. It will add a border to its children, grandchildren, etc so you can see what's up - great for precise layout tweaks.  It will also add flags if you made mistakes like put in inline styles, forgot an alt on an image, left the alt blank, etc.
      ul
        li Level 4
          span Level 5
        li Level 4
          span(style="") Level 5 w/ Inline style flag
        li Level 4
      h3 Images
      ul
        li
          p no alt tag:
          img(src='http://dogr.io/doge.png' width="150px" height="150px")         
        li
          p empty alt tag:
          img(src='http://dogr.io/doge.png' width="150px" height="150px" alt="")        
        li
          p all good:
          img(src='http://dogr.io/doge.png' width="150px" height="150px" alt="Alt tags for images")  
     
      h3 Links
      ul
        li
          a empty a tag    
        li
          a(href="#") I link to #
        li
          a(href="http://www.dbox.us" title="Check out my site.") I'm cool
!

CSS 

              
                // Mixin: Debug
//
// Debugging tool - adds a border to the current element, its children, 
// grandchildren, etc so you can see what's up – great for precise layout  
// tweaks.  It will also add flags if you made mistakes like put in inline 
// styles, forgot an alt on an image, left the alt blank, etc. Not to be used 
// in production, obviously.

debug()
  border 1px solid MediumPurple
  > *
    border 1px solid DarkKhaki
  > * > *
    border 1px solid MediumTurquoise
  > * > * > *
    border 1px solid LightSlateGray
  > * > * > * > *
    border 1px solid LightBlue
  > * > * > * > * > *
    border 1px solid MediumSlateBlue
  > * > * > * > * > * > *
    border 1px solid DeepSkyBlue
  > * > * > * > * > * > * > *
    border 1px solid DarkSeaGreen

  img
    border: 1px solid #f00
    -webkit-filter: hue-rotate(330deg) contrast(.75) saturate(6)
    filter: hue-rotate(330deg) contrast(.75) saturate(6)

  img[alt]
    border: 1px solid LimeGreen
    -webkit-filter: none
    filter: none

  img[alt=""]
    border: 1px solid gold
    -webkit-filter: contrast(1) saturate(2)
    filter: contrast(1) saturate(2)

  a
    background: rgba(#f00, .1)
    border: 1px solid #f00

  a[title]
    background: none
    border-color: LimeGreen

  style
    border: block

  [style], style, [class=""], [id=""], a[href="#"]
    background: rgba(yellow, .2)
    border: 1px solid gold

// call it
.debug
  debug()










// Demo styles only - Disregard

body
  font-family Helvetica, Arial, sans
  font-size 16px
  line-height 1.4em
  padding 2% 8%
  margin 0
  
*
  box-sizing border-box

 h1
  font-size 4.4vw
  font-weight normal
  line-height 1em
  margin 0

article
  width 60%
  margin 0 20%
  padding 4%

ul
  list-style-type none
  padding 3%
  margin 0
  overflow hidden

  > li
    display inline-block
    float left
    width calc(100% / 3)
    padding 2%

    a
      float right

    &:last-child
      margin-right 0

code
  background LightSlateGray 
  color white
!

JS
!
999px

Console