main content area width set based on container width

Created page twig to add the containers Closes #3511880

starshot_demo/templates/page.html.twig

+{#
+/**
+ * @file
+ * Claro's theme implementation to display a single Drupal page.
+ *
+ * The doctype, html, head, and body tags are not in this template. Instead
+ * they can be found in the html.html.twig template normally located in the
+ * core/modules/system directory.
+ *
+ * Available variables:
+ *
+ * General utility variables:
+ * - base_path: The base URL path of the Drupal installation. Will usually be
+ *   "/" unless you have installed Drupal in a sub-directory.
+ * - is_front: A flag indicating if the current page is the front page.
+ * - logged_in: A flag indicating if the user is registered and signed in.
+ * - is_admin: A flag indicating if the user has permission to access
+ *   administration pages.
+ *
+ * Site identity:
+ * - front_page: The URL of the front page. Use this instead of base_path when
+ *   linking to the front page. This includes the language domain or prefix.
+ *
+ * Page content (in order of occurrence in the default page.html.twig):
+ * - node: Fully loaded node, if there is an automatically-loaded node
+ *   associated with the page and the node ID is the second argument in the
+ *   page's path (e.g. node/12345 and node/12345/revisions, but not
+ *   comment/reply/12345).
+ *
+ * Regions:
+ * - page.header: Items for the header region.
+ * - page.pre_content: Items for the pre-content region.
+ * - page.breadcrumb: Items for the breadcrumb region.
+ * - page.highlighted: Items for the highlighted region.
+ * - page.help: Dynamic help text, mostly for admin pages.
+ * - page.content: The main content of the current page.
+ *
+ * @see template_preprocess_page()
+ * @see html.html.twig
+ */
+#}
+{% if page.header %}
+  <header>
+    {{ page.header }}
+  </header>
+{% endif %}
+<main>
+  <div class="visually-hidden"><a id="main-content" tabindex="-1"></a></div>
+
+  {% if page.banner %}
+    {{ page.banner }}
+  {% endif %}
+
+  {% if page.highlighted %}
+    {{ page.highlighted }}
+  {% endif %}
+
+  {% if page.content %}
+    <div class="ct-starshot-container--constrain">
+      <div class="ct-starshot-container__inner">
+        {{ page.content }}
+      </div>
+    </div>
+  {% endif %} 
+
+  {% if page.sidebar %}
+    {{ page.sidebar }}
+  {% endif %}
+
+  {% if page.footer %}
+    {{ page.footer }}
+  {% endif %}
+</main>