First commit.

sass/components/header/_header.scss

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+// Dependencies.
+@import 'base/headings/headings';
+@import 'components/clearfix/clearfix';
+
+// Branding header
+//
+// Markup: header.twig
+//
+// Style guide: components.header
+
+.header,
+%header {
+  @extend %clearfix;
+
+  // Wrapping link for logo.
+  &__logo {
+    float: left;
+    margin: 0 10px 0 0;
+    padding: 0;
+
+    @include rtl() {
+      float: right;
+      margin: 0 0 0 10px;
+    }
+  }
+
+  // Logo image.
+  &__logo-image {
+    vertical-align: bottom;
+  }
+
+  // Wrapper for website name and slogan.
+  &__name-and-slogan {
+    float: left;
+  }
+
+  // The name of the website.
+  &__site-name {
+    @extend %h1;
+    margin: 0;
+  }
+
+  // The link around the name of the website.
+  &__site-link {
+    &:link,
+    &:visited {
+      color: color(text);
+      text-decoration: none;
+    }
+
+    &:hover,
+    &:focus {
+      text-decoration: underline;
+    }
+  }
+
+  // The slogan (or tagline) of a website.
+  &__site-slogan {
+    margin: 0;
+  }
+
+  // The secondary menu (login, etc.)
+  &__secondary-menu {
+    float: right;
+
+    @include rtl() {
+      float: left;
+    }
+  }
+
+  // Wrapper for any blocks placed in the header region.
+  &__region {
+    // Clear the logo.
+    clear: both;
+  }
+}

sass/components/header/header.twig

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+<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>