{source}
  <?php
    // Get the ID of the category you want to display
    $category_id = 1;

    // Get the articles from the category
    $db = JFactory::getDbo();
    $query = $db->getQuery(true)
      ->select($db->quoteName(array('id', 'title', 'introtext')))
      ->from($db->quoteName('#__content'))
      ->where($db->quoteName('catid') . ' = ' . (int) $category_id);
    $db->setQuery($query);
    $articles = $db->loadObjectList();
  ?>

  <style>
  .ticker {
    width: 100%;
    overflow: hidden;
    position: relative;
  }

  .ticker ul {
    display: flex;
    position: absolute;
    white-space: nowrap;
    animation: ticker 10s linear infinite;
  }

  .ticker li {
    display: inline-block;
    padding: 0 20px;
    min-width: 500px;
  }

  @keyframes ticker {
    0% {
      transform: translate3d(0, 0, 0);
    }
    100% {
      transform: translate3d(-100%, 0, 0);
    }
  }
  </style>

  <div class="ticker">
    <ul>
      {source}
        <?php
          // Output the articles
          foreach ($articles as $article) {
            echo '<li>' . $article->introtext . '</li>';
          }
        ?>
      {/source}
    </ul>
  </div>
{/source}