<body>
        <header class="header">
        <ul class="menu">
          <li><a class="menu_link" href="#">Acceuil</a></li>
          <li><a class="menu_link" href="#">Blog</a></li>
          <li><a class="menu_link" href="#">About</a></li>
          <li><a class="menu_link" href="#">Portfolio</a></li>
          <li><a class="menu_link" href="#">Contact</a></li>
        </ul>
      </header>
      <main class="h-200">
    <h1>L'interMEDIAire</h1>
    <h2>Titre 2</h2>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quibusdam ipsam delectus sapiente officia temporibus quam dolorum nam iusto asperiores vitae, quia, ratione hic quod vel unde quae tempore a in.Earum sapiente cupiditate ducimus amet quo provident! Adipisci eaque ducimus incidunt tempora ipsa? Iusto, repellat aliquam reprehenderit fugit! Perspiciatis, reprehenderit quisquam excepturi!</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsum velit nam illo molestiae earum, distinctio recusandae omnis eius soluta. Saepe asperiores libero modi est eum rem aliquid dolorum laudantium magnam.</p>
        <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quibusdam ipsam delectus sapiente officia temporibus quam dolorum nam iusto asperiores vitae, quia, ratione hic quod vel unde quae tempore a in.Earum sapiente cupiditate ducimus amet quo provident! Adipisci eaque ducimus incidunt tempora ipsa? Iusto, repellat aliquam reprehenderit fugit! Perspiciatis, reprehenderit quisquam excepturi!</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsum velit nam illo molestiae earum, distinctio recusandae omnis eius soluta. Saepe asperiores libero modi est eum rem aliquid dolorum laudantium magnam.</p>
        <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quibusdam ipsam delectus sapiente officia temporibus quam dolorum nam iusto asperiores vitae, quia, ratione hic quod vel unde quae tempore a in.Earum sapiente cupiditate ducimus amet quo provident! Adipisci eaque ducimus incidunt tempora ipsa? Iusto, repellat aliquam reprehenderit fugit! Perspiciatis, reprehenderit quisquam excepturi!</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsum velit nam illo molestiae earum, distinctio recusandae omnis eius soluta. Saepe asperiores libero modi est eum rem aliquid dolorum laudantium magnam.</p>
        <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quibusdam ipsam delectus sapiente officia temporibus quam dolorum nam iusto asperiores vitae, quia, ratione hic quod vel unde quae tempore a in.Earum sapiente cupiditate ducimus amet quo provident! Adipisci eaque ducimus incidunt tempora ipsa? Iusto, repellat aliquam reprehenderit fugit! Perspiciatis, reprehenderit quisquam excepturi!</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsum velit nam illo molestiae earum, distinctio recusandae omnis eius soluta. Saepe asperiores libero modi est eum rem aliquid dolorum laudantium magnam.</p>
        <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quibusdam ipsam delectus sapiente officia temporibus quam dolorum nam iusto asperiores vitae, quia, ratione hic quod vel unde quae tempore a in.Earum sapiente cupiditate ducimus amet quo provident! Adipisci eaque ducimus incidunt tempora ipsa? Iusto, repellat aliquam reprehenderit fugit! Perspiciatis, reprehenderit quisquam excepturi!</p>
  </main>
</body>
/*COULEURS*/
$noir:        rgba(0,0,0,1);
$noirfonce:   rgba(29,31,32,1);
$noiropaque:  rgba(29,31,32,.9);
$rose:        rgba(152,38,114,1);
$bleu:        rgba(128,155,189,1);
$blanc:       rgba(255,255,255,1);
$gris:        rgba(55,55,55,1);
$gris2:       rgba(255,255,255,.8);
$gris3:       rgba(204,204,204,1);
$padding:     20px 10px;

/*TOUS LES ELEMENTS*/
*,*:after,*:before {
  box-sizing: border-box;
  -moz-box-sizing: border-box;
  -webkit-box-sizing: border-box;
}

body {
  margin: 0px auto;
  padding: $padding;
  background: $noir;
  color: $blanc;
  font-size: 1em;
}

main {
  margin: auto;
  padding: $padding;
  width: 640px;
  background: $noirfonce;
}

h1 {
  margin: 0;
  padding: 0;
  font-size: 1.4em;
  color: $bleu;
}

p {
  line-height: 150%;
}

h2 {
  margin-top: 15px;
  width: 100%;
  color: $rose;
}

h1,h2 {
  font-family: 'Inconsolata', monospace;
}

a {
  text-decoration: none;
  transition: opacity .3s ease;

  &:hover,
  &:active {
    opacity: .75;
    transition: opacity .3s ease;
  }
}

%transition {
  transition: position .3s ease;
  transition: background .5s ease;
  transition: height .7s ease;
}

.header {
  position: relative;
  width: 100%;
  height: 100px;
  background: black;
  @extend %transition;

  &.sticky {
    position: fixed;
    top: 0px;
    height: 60px;
    @extend %transition;
    
    a {
      color: white;
    }
  }
}

.menu {
  display: flex;
  justify-content: center;
  align-items: center;
  padding: none;
  height: 100%;
}

.menu_link {
  margin-right: 24px;
  color: white;
  font-size: 1.2em;
  font-family: serif;
  transition: all .9s ease;

  .sticky & {
    margin-right: 12px;
    color: black;
    font-size: 1em;
    font-family: sans-serif;
    transition: all .9s ease;
  }
}

.h-200 {
  height: 200vh;
}
/*www.lintermediaire.be*/
View Compiled 
$(document).ready(function() {
  $(window).on("scroll", function() {
    var $header = $('.header'),
        heightHeader = $header.height();
    if($(this).scrollTop() > (heightHeader)) {
      $header.addClass('sticky');
    }
    else {
      $header.removeClass('sticky');
    }
  });
});

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.1/jquery.min.js