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HTML

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About the <head>

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Insecure Resource

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CSS

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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

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About Vendor Prefixing

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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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HTML 

              
                section#section1
  .section-grid
    .left
      .grid-text
        p Lorem, ipsum dolor sit amet consectetur adipisicing elit. Facilis consequuntur officia laboriosam error. Illum numquam est labore suscipit deserunt voluptate aspernatur dolorem, ipsam recusandae cupiditate itaque omnis eum fuga iste?
    .right
      .grid-image.image-1.active
        img(src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/495197/0st9yhngses-benjamin-child.jpg")

section#section2
  .section-grid
    .left
      .grid-text
        p Lorem, ipsum dolor sit amet consectetur adipisicing elit. Facilis consequuntur officia laboriosam error. Illum numquam est labore suscipit deserunt voluptate aspernatur dolorem, ipsam recusandae cupiditate itaque omnis eum fuga iste?
    .right
      .grid-image.image-2.active
        img(src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/495197/2fgvaqx-fxs-oskar-krawczyk.jpg")

section#section3
  .section-grid
    .left
      .grid-text
        p Lorem, ipsum dolor sit amet consectetur adipisicing elit. Facilis consequuntur officia laboriosam error. Illum numquam est labore suscipit deserunt voluptate aspernatur dolorem, ipsam recusandae cupiditate itaque omnis eum fuga iste?
    .right
      .grid-image.image-3.active
        img(src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/495197/Great_Wave_off_Kanagawa2_cr.jpg")
!

CSS 

              
                @import url("https://fonts.googleapis.com/css?family=Montserrat:400,400i,700")

body
  font-family: Montserrat, sans-serif
  line-height: 1.4

img
  width: 200px
  display: block
  box-shadow: 0px 0px 30px 0px rgba(black, 0.3)
  
  @media (min-width: 700px)
    width: 400px
    
  @media (min-width: 1000px)
    width: 600px
  
.section-grid
  display: grid
  // Responsive, 1/3 - 2/3 split
  grid-template-columns: 1fr 2fr
  height: 100vh
  
.left,
.right
  // Center the elements in each column
  display: flex
  justify-content: center
  align-items: center
  
.grid-text
  padding: 1rem
  position: relative
  // Flexbox centers the paragraph element
  display: flex
  justify-content: center
  align-items: center
  height: 100%

.grid-image
  // keeps the image fixed on scroll
  position: fixed
  z-index: 100
  
.image-1,
.image-2,
.image-3
  opacity: 0
  
  &.active
    animation: fadeIn 1000ms ease forwards
    opacity: 1
    
    
@keyframes fadeIn 
  0%
    opacity: 0
  100%
    opacity: 1
!

JS 

              
                // find the top of each section
var section1 = $('#section1').offset().top;
var section2 = $('#section2').offset().top;
var section3 = $('#section3').offset().top;

// number of pixels before the section to change image
var scrollOffset = 300;


// run this function when the window scrolls
$(window).scroll(function() {  
  
   
  // get the window height on scroll
  var scroll = $(window).scrollTop() + scrollOffset;  
  

  // if scroll hits the top of section 1  
  if ( scroll < 500 ) {
    $('.grid-image img').attr('src', 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/495197/0st9yhngses-benjamin-child.jpg');
  }
  
  // if scroll hits the top of section 2
  if ( scroll > section2 ) {
    $('.grid-image img').attr('src', 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/495197/2fgvaqx-fxs-oskar-krawczyk.jpg');
  }

  // if scroll hits the top of section 3
  if ( scroll > section3 ) {
    $('.grid-image img').attr('src', 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/495197/Great_Wave_off_Kanagawa2_cr.jpg');
  }
});
!
999px

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