If you're looking to toggle classes, it's recommended to avoid using fadeIn and fadeOut. Here are some alternatives.
CSS
#first {
background-color: red;
height: 250px;
opacity: 1;
-webkit-transition: .25s all ease;
-moz-transition: .25s all ease;
-ms-transition: .25s all ease;
-o-transition: .25s all ease;
transition: .25s all ease;
}
#second {
background-color: green;
height: 250px;
opacity: 1;
-webkit-transition: .25s all ease;
-moz-transition: .25s all ease;
-ms-transition: .25s all ease;
-o-transition: .25s all ease;
transition: .25s all ease;
}
.hidden {
height: 0 !important;
opacity: 0 !important;
}
HTML
<section id="parent">
<div id="first">
Lorem ipsum dolor sit amet, consectetur adipisicing elit. Accusamus sequi iure, nesciunt laudantium a beatae autem, commodi culpa, quasi vitae sint ad. Itaque repellat cum voluptate, est aut provident ipsum?
</div>
<div id="second" class="hidden">
Lorem ipsum dolor sit amet, consectetur adipisicing elit. Accusamus sequi iure, nesciunt laudantium a beatae autem, commodi culpa, quasi vitae sint ad. Itaque repellat cum voluptate, est aut provident ipsum?
</div>
</section>
Javascript
jQuery(document).ready(function(){
$('body').click(function(){
$('#first, #second').toggleClass('hidden');
});
});
Fiddle Link : https://jsfiddle.net/bngnxty9/
You can customize the event trigger in the script according to your needs.