GNWT Base Theme Style Guide

Example
Markup: components/header/header.twig
<header class="header {{modifier_class}}" role="banner">
  <a href="/" title="Home" rel="home" class="header__logo">
    <img src="kss-assets/sample-inline.png" alt="Home" class="header__logo-image">
  </a>

  <div class="header__name-and-slogan">
    <h1 class="header__site-name">
      <a href="/" title="Home" class="header__site-link" rel="home">Site Name</a>
    </h1>
    <div class="header__site-slogan">Slogan</div>
  </div>

  <nav class="header__secondary-menu" role="navigation">
    <h2 class="visually-hidden">User menu</h2>
    <ul class="links inline clearfix">
      <li class="menu-2 first"><a href="/user">My account</a></li>
      <li class="menu-15 last"><a href="/user/logout">Log out</a></li>
    </ul>
  </nav>

  <div class="header__region">
    [Header region]
  </div>
</header>
Source: sass/components/header/_header.scss, line 5