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CSS

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HTML 

              
                <div class="content-wrapper">
  <h1 class="title">Lorem ipsum dolor sit amet</h1>

  <nav class="left-nav">
    <ul class="left-nav__list">
      <li class="left-nav__list-item"><a href="#" class="left-nav__link">Lorem ipsum dolor.</a></li>
      <li class="left-nav__list-item"><a href="#" class="left-nav__link">Non, officiis iusto.</a></li>
      <li class="left-nav__list-item"><a href="#" class="left-nav__link">Sed, velit, ullam?</a></li>
      <li class="left-nav__list-item"><a href="#" class="left-nav__link">Nobis itaque, ad!</a></li>
      <li class="left-nav__list-item"><a href="#" class="left-nav__link">Explicabo provident, sit.</a></li>
      <li class="left-nav__list-item"><a href="#" class="left-nav__link">Modi, cum, nam!</a></li>
      <li class="left-nav__list-item"><a href="#" class="left-nav__link">Tempora, quo illum?</a></li>
      <li class="left-nav__list-item"><a href="#" class="left-nav__link">Dolore, harum, quidem!</a></li>
    </ul>
  </nav>

  <div class="reading-column">
    <div class="reading-column__section">
      <h2 class="reading-column__title">Lorem ipsum dolor sit amet, consectetur.</h2>
      <p class="reading-column__desc">Lorem ipsum dolor sit amet, consectetur adipisicing elit. Eius est tenetur possimus ipsum. Nostrum nobis odit delectus et excepturi, quis repudiandae facere, expedita dignissimos, quo nihil? Veritatis, voluptates expedita corporis earum esse illo ipsa vitae ab. Molestiae officiis officia aut? Explicabo earum quis officia quo eligendi eveniet reprehenderit sint dolores?</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Nostrum reprehenderit nam, reiciendis explicabo suscipit!</h2>
      <p class="reading-column__desc">Deserunt nesciunt qui illo corporis maxime, impedit veritatis blanditiis magni dolor! Commodi aliquam deserunt neque dicta sequi veniam quia molestias non earum illum, mollitia qui modi doloribus accusantium, explicabo, hic possimus eos dolore dignissimos repellendus similique facilis fuga fugit? Eum earum eaque enim, laboriosam culpa nemo perspiciatis alias veniam quasi?</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Ipsa nihil ullam, in velit nesciunt.</h2>
      <p class="reading-column__desc">Earum rerum, exercitationem. Aut numquam unde magnam accusantium praesentium nisi quae ipsum similique consequatur magni debitis, tenetur incidunt beatae explicabo fuga doloremque quisquam consectetur, necessitatibus. Quibusdam quos corrupti veniam repudiandae aut sunt quo officiis ab nam iusto temporibus ipsum laboriosam omnis, aperiam ad, quod harum facilis facere mollitia recusandae eveniet!</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Quas ducimus quod, nisi iste. Labore.</h2>
      <p class="reading-column__desc">Est quo vero perspiciatis explicabo ab suscipit, tempora dignissimos. Quae modi molestias, velit accusamus perspiciatis vero quia blanditiis! Ullam qui vel soluta perferendis necessitatibus odio esse labore quos sint officiis cum debitis provident voluptas incidunt, doloremque accusantium distinctio praesentium error voluptatibus amet fugiat. Expedita, molestiae, vel. Suscipit debitis, minima laborum?</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Ipsa quae voluptas, deleniti commodi in!</h2>
      <p class="reading-column__desc">Reiciendis temporibus nostrum voluptatum quas recusandae neque alias rerum provident asperiores optio dolore laboriosam eaque, quos doloribus perferendis nisi nesciunt, sint ducimus sit quasi pariatur ratione. Pariatur nam laboriosam debitis eligendi officia, consequuntur, deserunt ullam, illum earum quo, vel sit modi harum velit et! Quis, atque qui. Rerum, dolor, inventore!</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Libero similique quas rerum quia autem.</h2>
      <p class="reading-column__desc">Necessitatibus, animi, sequi. Iure officia architecto ullam quia pariatur accusamus quae repellendus accusantium id ducimus minima, necessitatibus voluptas dignissimos a praesentium, odit cum. Sint nobis, natus esse quam nam ea enim magni nulla! Doloribus ducimus, aliquam voluptatibus ad excepturi, minus, vitae nostrum maiores iure suscipit impedit. Quae labore, aliquam deserunt?</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Laboriosam illum deleniti saepe ducimus ullam.</h2>
      <p class="reading-column__desc">Dignissimos omnis accusamus excepturi molestias iusto totam vero corporis aliquid consequuntur. Nobis voluptates quidem, magni. Ratione dolorum nihil quod commodi officia quisquam quis dolores. Unde, corporis, voluptas! Earum ab placeat incidunt quae, iste nulla molestiae, ipsa est officia soluta inventore commodi eveniet repudiandae exercitationem debitis aliquid, minima libero asperiores repellat.</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Non, ipsam eligendi saepe molestiae praesentium!</h2>
      <p class="reading-column__desc">Ullam beatae nobis facilis, hic atque. Culpa soluta in iure accusantium consequuntur minima illo qui eligendi reprehenderit non labore earum et alias recusandae consectetur enim aut fuga vero aperiam cupiditate voluptates iste perspiciatis, blanditiis. Obcaecati minima dolore laudantium provident! Praesentium hic tempora laudantium nobis molestias eligendi corporis veniam delectus ut.</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Voluptatum eum saepe commodi ad ea.</h2>
      <p class="reading-column__desc">Necessitatibus dolore iste neque voluptates, aspernatur magni! Eos quam neque, laboriosam quas excepturi recusandae eius iusto repudiandae eveniet blanditiis saepe ratione quibusdam obcaecati animi ad voluptate sunt fugit aut eum facere sequi perspiciatis iure numquam dolorum voluptatum! Facilis error minus temporibus quis, cumque incidunt? Repudiandae odit, optio consequatur excepturi inventore!</p>
    </div>
    <div class="reading-column__section">
      <h2 class="reading-column__title">Repudiandae quos nemo est assumenda molestiae!</h2>
      <p class="reading-column__desc">Consequuntur deserunt quod dicta ipsa cumque fugiat asperiores perferendis nesciunt officiis dolorum mollitia, repellendus dolore quasi optio provident, quia ut sunt a velit fuga aliquid aut ducimus culpa! Porro assumenda quis, delectus quaerat dolores sint officia, minus labore quisquam vel deleniti, itaque placeat repudiandae at neque perferendis voluptatem quas quibusdam.</p>
    </div>
  </div>
</div>
!

CSS 

              
                * {
  box-sizing: border-box;
}

body {
  font-family: sans-serif;
  // font-size: 18px;
  line-height: 1.5;
  margin: 2rem;
}

img {
  width: 100%;
}

.content-wrapper {
  display: grid;
  grid-gap: 0 2rem;
  grid-template-areas:
    ". title"
    "leftnav reading";
  grid-template-columns: minmax(250px, 1fr) 3fr;
  width: 100%;
}

.title {
  grid-area: title;
}

.left-nav {
  grid-area: leftnav;
  position: relative;
  max-width: 100%;
}

.left-nav__list {
  list-style-type: none;
  padding: 0;
  text-align: right;
  position: sticky;
  top: 0;
}

.left-nav__list-item {
  line-height: 2;
}

.reading-column {
  grid-area: reading;
}

.reading-column__section {
  width: 100%;
  max-width: 60ch;
}

@media only screen and (max-width: 900px) {
  .content-wrapper {
    grid-template-areas:
      "title"
      "leftnav"
      "reading";
    grid-template-columns: 1fr;
  }
  
  .left-nav {
    width: auto;
  }

  .left-nav__list {
    text-align: left;
  }
}
!

JS
!
999px

Console