Update default.html

Author: jalammar

_layouts/default.html

@@ -77,8 +77,9 @@ <h1 class="site-name"><a href="{{ site.baseurl }}/">{{ site.name }}</a></h1>
       {{ content }}
     </div>
 
-<iframe src="https://newsletter.languagemodels.co/embed" width="480" height="320" style="border:1px solid #EEE; background:white;" frameborder="0" scrolling="no"></iframe>
-
+    <div style="display: flex; justify-content: center; align-items: center; margin-top: 20px;">
+  <iframe src="https://newsletter.languagemodels.co/embed" width="480" height="320" style="border:1px solid #EEE; background:white;" frameborder="0" scrolling="no"></iframe>
+    </div>
 
 <div style="padding: 10px 0 10px 3%; color: #555; font-size:85%">
 <a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-nc-sa/4.0/88x31.png" /></a><br />This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License</a>.