--- /dev/null
+{#
+/**
+ * @file
+ * Default theme implementation to display a one-column layout.
+ *
+ * Available variables:
+ * - content: The content for this layout.
+ * - attributes: HTML attributes for the layout <div>.
+ *
+ * @ingroup themeable
+ */
+#}
+{%
+ set classes = [
+ 'layout',
+ 'layout--onecol',
+ ]
+%}
+{% if content %}
+ <div{{ attributes.addClass(classes) }}>
+ <div {{ region_attributes.content.addClass('layout__region', 'layout__region--content') }}>
+ {{ content.content }}
+ </div>
+ </div>
+{% endif %}