Left-align all blog pages

Apply left-alignment to both blog listing and individual blog posts,
while keeping other pages (home, etc.) centered

Author: Hasaber8

layouts/partials/custom_head.html

@@ -0,0 +1,9 @@
+<style>
+  /* Left-align all blog pages (listing and posts) */
+  {{ if eq .Section "blog" }}
+  body {
+    margin-left: 20px;
+    margin-right: auto;
+  }
+  {{ end }}
+</style>