JSFiddle - React, Tailwind, and code Playground

by Egor Jsfiddle

HTML

<header>
  <div id="main_nav">
    <div class="circle"></div>
    <nav>
      <a href="#">HOME</a>
      <a href="#">ABOUT</a>
      <a href="#">CONTACT</a>
    </nav>
    </div>
</header>
<div class="da">
  <div>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Totam praesentium suscipit placeat exercitationem, libero ipsam deleniti non mollitia reprehenderit sequi, aliquid id molestias! Unde non nisi ratione eum, totam cupiditate!</div>
  <div>Magni ab nisi iusto maxime dolore nihil minus praesentium dignissimos, quaerat beatae sapiente aperiam blanditiis incidunt libero saepe repellendus nesciunt temporibus iste. Delectus velit, laudantium cum minus quod, accusantium ipsum.</div>
  <div>Delectus obcaecati numquam consequuntur maxime natus, nostrum tenetur rem sapiente quos aliquid unde quia eveniet non repellat repellendus iste enim odio itaque officiis doloremque illum repudiandae veritatis. Dolorem, magni, dolorum.</div>
  <div>Voluptatum officiis tempora amet minus reprehenderit temporibus quia, optio dicta quod harum perspiciatis porro odit unde vero ipsa ex maiores deserunt voluptate incidunt quidem dolores? Maiores, facilis veritatis at illo?</div>
  <div>Veniam, ut iure? At ipsa quaerat corrupti sed ipsam, modi sit esse cumque, fugiat ut natus culpa dolore rem perspiciatis possimus necessitatibus consequuntur itaque totam aspernatur doloribus asperiores quisquam dolorem.</div>
  <div>Iusto, delectus veniam, blanditiis voluptates totam non voluptatum doloribus nihil facilis maxime sit aspernatur architecto tempora rerum culpa labore nisi cum, ad quibusdam qui tempore praesentium accusamus suscipit. Omnis, ratione?</div>
  <div>Quasi cupiditate eveniet, corporis corrupti ipsa eos animi saepe maiores quas voluptatum debitis placeat sed praesentium velit quam sit, eligendi, quae aliquid fugiat, impedit. Velit odio suscipit nemo eveniet error.</div>
  <div>Odit porro a officiis enim recusandae eos, commodi, temporibus cumque quis, fuga aliquid!...

CSS

body {
  background: #060606;
}

header {
  overflow: hidden;
  background: url(img/bg.png) no-repeat center bottom / cover;
  min-height: 100%;
  position: relative;
}

header #main_nav {
  margin: 0 3%;
  padding: 30px 0 35px 0;
  display: flex;
  flex-flow: row wrap;
  justify-content: space-between;
  border-bottom: 1px solid rgba(255, 255, 255, .3);
}

header > div .circle {
  border: 2px solid #fff;
  border-radius: 50px;
  width: 20px;
  height: 20px;
}

header nav a {
  font: .8em 'montserratbold';
  color: #fff;
  margin: 0 10px;
  text-decoration: none;
}

/* header nav a:hover {
  color: grey;
}

header .gam_menu button {
  background: transparent;
  color: #fff;
  border: 0;
  cursor: pointer;
  margin: 0 0 0 25px;
  padding: 5px;
}

header #hide_menu {
  background: rgba(0, 0, 0, .8);
  color: #fff;
  width: 250px;
  height: 100%;
  position: absolute;
  z-index: 2;
  top: 0;
  right: -300px;
  -webkit-transition: all .5s ease;
  -o-transition: all .5s ease;
  transition: all .5s ease;
}

header #hide_menu ul {
  padding: 0 0 0 20px;
  list-style: none;
}

header #hide_menu ul li {
  padding: 5px 0;
  margin: 0 5px;
}

header #hide_menu ul a {
  text-decoration: none;
  padding: 5px 0;
  color: #fff;
}

header #hide_menu i {
  cursor: pointer;
  padding: 10px;
}

.disactive {
  -webkit-transform: translate(-300px, 0px);
  -ms-transform: translate(-300px, 0px);
  -o-transform: translate(-300px, 0px);
  transform: translate(-300px, 0px);
}

header h1 {
  font: 5em 'playfair_displayregular';
  margin: 0;
  color: #fff;
}

header p {
  font: .7em/2 'montserratlight';
  margin: 0 35%;
  display: inline-block;
  color: #fff;
}

header .losng {
  margin: 10% 0 0 0;
}

header .losng button {
  background: #da7074;
  border-radius: 15px;
  border: none;
  padding: 10px 25px;
  color: #fff;
  font: .7em 'montserratbold';
  margin: 40px 0 0 0;
  position: relative;
  z-index: 1;
  cursor: pointer;
}

header .losng button span {
  position: absolute;
  content:...

JavaScript

var nav = document.getElementById("main_nav").offsetHeight;
	// console.log(nav);

	window.onscroll = function() {
	  var scrolled = window.pageYOffset || document.documentElement.scrollTop;
	  var head = document.getElementsByTagName("header");
	  // document.getElementById('showScroll')
	  if (scrolled > nav) {
	  	$("#main_nav").addClass("scrollt");
	  	// $("header ").prepend("<p>А вот оно че</p>");
	  }
	  else
	  	$("#main_nav").removeClass("scrollt");
	}