Use semantic HTML

_layouts/post.html

@@ -1,12 +1,12 @@
 ---
 layout: default
 ---
-<header>
-  <h1>{{ page.title }}</h1>
-  <span class="post-date">{{ page.date | date: "%A, %B %d %Y" }}</span>
-</header>
-<hr>
+<article>
+  <header>
+    <h1 class="post-title">{{ page.title }}</h1>
+    <time datetime="{{ page.date | date: '%y-%m-%d' }}" class="post-date">{{ page.date | date: "%A, %B %d %Y" }}</time>
+  </header>
+  <hr>
 
-<div class="article">
   {{ content }}
-</div>
+</article>