JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
    <p>...</p>
</div>

CSS

html {
    background-repeat: no-repeat;
    background-position: center center;
    background-attachment: fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}

html {
    background-image:url(http://i.imgur.com/ZhVps3b.jpg?1);
    -webkit-transition: all 1s ease;/* Safari & Chrome */
-moz-transition: all 1s ease;/* Firefox */
-o-transition: all 1s ease;/* Opera */
transition: all 1s ease;
}

html.scrolled {
    background-image:url(http://i.imgur.com/h6rmrc0.png?1);
    -webkit-transition: all 1s ease;/* Safari & Chrome */
-moz-transition: all 1s ease;/* Firefox */
-o-transition: all 1s ease;/* Opera */
transition: all 1s ease;
}

JavaScript

jQuery(window).scroll(function(){
    var fromTopPx = 200; // distance to trigger
    var scrolledFromtop = jQuery(window).scrollTop();
    if(scrolledFromtop > fromTopPx){
        jQuery('html').addClass('scrolled');
    }else{
        jQuery('html').removeClass('scrolled');
    }
});