<html>
  <head>
    <title>Sticky Navigation Example</title>
  </head>
  <body>
    <header>
      <div class="navigation">
        <ul>
          <li><a href="#">Home</a></li>
          <li><a href="#">About</a></li>
          <li><a href="#">Services</a></li>
          <li><a href="#">Contact Us</a></li>
        </ul>
    </header>
  </body>
</html>
body{
  margin:0;
  padding:0;
}
header{
  height:500px;
  background:url('https://via.placeholder.com/2048x2048') center no-repeat;
  background-size:cover;
}

body{
  /* Default navigation styling inside body tag */
  .navigation{
    background:#000;
    ul{
      list-style:none;
      text-align:center;
      margin:0;
      li{
        display:inline-block;
        a{
          display:block;
          padding:10px 10px;
          color:#fff;
          text-decoration:none;
          text-transform:uppercase;
        }
      }
    }
  }
  /* Additional/updated Navigation styling inside body tag with class "scrolled" */
  &.scrolled{
    .navigation{
      position:fixed;
      width:100%;
    }
  }
}
View Compiled
/* function to add 'scrolled' class in body tag when user scroll value is more than 200px */
function manageNavbar(){
  var scroll = $(window).scrollTop();
  if( scroll >= 200){
    $('body').addClass('scrolled');
  } else { // if scroll value goes less than 200px
    //remove 'scrolled' class from body tag
    $('body').removeClass('scrolled');
  }
}

$(document).ready(function(){
  manageNavbar();
});
$(window).scroll(function(){
  manageNavbar();
});
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External CSS

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External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js