Short CODE

By Julius Timgum

PHP CODE 

function custom_author_box() {
    ob_start();
    ?>
    <div class="custom-author-box">
        <div class="author-avatar">
            <?php echo get_avatar(get_the_author_meta('ID'), 96); ?>
        </div>
        <div class="author-name">
            <p>Written by <strong><?php the_author(); ?></strong></p>
        </div>
    </div>
    <?php
    return ob_get_clean();
}
add_shortcode('author_box', 'custom_author_box');

CSS CODE (optional)

.custom-author-box {
  display: flex;
  align-items: center;
  margin-top: 30px;
  padding-top: 20px;
  border-top: 1px solid #fb3365;
}
.custom-author-box .author-avatar {
  margin-right: 15px;
}
.custom-author-box img {
  border-radius: 50%;
  width: 80px;
  height: 80px;
}
.custom-author-box .author-name {
  font-size: 16px;
}