Product Landing Page - Build a Product Landing Page - 3X25DJpPTH2qVjkDohO7d

i can’t seem to make my landing page responsive,it is not fitting for smaller size

<!DOCTYPE html>
<html>
  <head>
    <meta charset='UTF-8'>
    <meta name='viewport' content='width=device-width, initial-scale='1.0'>
    <link rel='stylesheet' href='styles.css'>
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
    <title>Product Landing Page</title>
  </head>
  <body>
    <main>
      <header id='header'>
       <img src='https://cdn.freecodecamp.org/testable-projects-fcc/images/product-landing-page-logo.png'id='header-img' alt='logo'>
       <nav id='nav-bar'>
         <ul>
           <li><a href='#features'class='nav-link'>Features</a></li>
           <li><a href='#how-it-works' class='nav-link'>How it works</a></li>
 <li><a href='#pricing'class='nav-link' >Pricing</a></li>
       </nav>
      </header>
      <div id='content'>
        <div>
       <h1>Handcrafted, home-made masterpieces<h1> 
         <form id='form' action='https://www.freecodecamp.com/email-submit'><input type='email' name='email'  id='email' placeholder='Enter email address'>
         <input type='submit' value='GET STARTED' id='submit'>
         </form>
      </div>

      <div id='features'>
        <div>
           <div class='fire'><i class='fa fa-fire fa-3x'></i></div>
         <div class='features-list' > 
<h2>Premium Materials</h2>
<p>Our trombones use the shiniest brass which is sourced locally. This will increase the longevity of your purchase.</p></div>
</div>
<div>
   <div class='truck'><i class='fa fa-truck fa-3x fa-flip-horizontal'></i></div>
  <div class='features-list'><h2>Fast Shipping</h2>
        <p>We make sure you recieve your trombone as soon as we have finished making it. We also provide free returns if you are not satisfied.</p></div>
        </div>

        <div>
<div class='battery'><i class='fa fa-battery fa-3x'></i></div>
        <div class='features-list' ><h2>Quality Assurance</h2>
           <p>For every purchase you make, we will ensure there are no damages or faults and we will check and test the pitch of your instrument.</p></div>
  </div>
      </div>
      
      <div id='how-it-works'>
       <iframe id='video' width='500' height='400' src='https://www.youtube.com/embed/y8Yv4pnO7qc'></iframe>
      </div>
      <div id='pricing'> 
<div class=' tenor trombone'>
  <div class='type'>TENOR TROMBONE</div>
  <p class='price'>$600</p>
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<p>Lorem ipsum.</p>
<button type='button'>SELECT</button>
</div>
<div class=' bass trombone' >
  <div class='type'>BASS TROMBONE</div>
  <p class='price'>$900</p>
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<button type='button'>SELECT</button>
</div>

<div class=' valve trombone'>
  <div class='type' >VALVE TROMBONE</div>
  <p class='price'>$1200</p>
<p>Plays similar to a Trumpet</p>
<p>Great for Jazz Bands</p>
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<button type='button'>SELECT</button>
</div>
      </div>
      <footer>
        <ul>
          <li><a href='#privacy'>Privacy</a></li>
          <li><a href='#terms'>Terms</a></li>
          <li><a href='#conditions'>Contact</a></li>
        </ul>
        <p>Copyright 2016, Original Trombones</p>
      </footer>
      <div>
    </main>
  </body>
</html>

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Challenge: Product Landing Page - Build a Product Landing Page

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