easy-going-rails/app/views/layouts/_navbar.html.erb

<nav>
  <ul>
    <li>
      A<%=fa_icon :eye, size: '4x'%>
      B<%=fa_icon :user, size: '4x'%>
      <%=fa_icon :user, class: 'text-blue-400', style: :regular, size: '10x'  %>
      <%=fa_icon :user, class: 'text-blue-400', size: '10x'  %>
      <%=fa_icon :user, size: '10x'  %>
    </li>
    <li>C<i class="fa-regular fa-user"></i></li>
    <li>D<i class="fa-solid fa-user"></i></li>
  </ul>

  <!-- solid style -->
  <i class="fa-solid fa-user"></i>

  <!-- regular style -->
  <i class="fa-regular fa-user"></i>

  <!--brand icon-->
  <i class="fa-brands fa-github-square"></i>
</nav>