Update style of grouping headers in blog and index

layouts/index.html

@@ -11,7 +11,9 @@
             <ul>
             {{ range first 5 (.Data.Pages.GroupByDate "Jan, 2006" "desc")}}
                 {{ $nbPages := len (where .Pages "Section" "blog")}}
-                {{ if ne $nbPages 0}}{{ .Key }}{{ end }}
+                {{ if ne $nbPages 0}}
+                    <li class="groupby">{{ .Key }}</li>
+                {{ end }}
                 {{ range where .Pages.ByPublishDate "Section" "blog"}}
                     {{ partial "li.html" . }}
                 {{ end }}

layouts/section/blog.html

@@ -5,7 +5,7 @@
             <div class="page-heading">Blog</div>
             <ul>
                 {{ range .Data.Pages.GroupByDate "Jan, 2006" "desc"}}
-                    {{ .Key }}
+                    <li class="groupby">{{ .Key }}</li>
                     {{ range .Pages.ByPublishDate }}
                         {{ partial "li.html" . }}
                     {{ end }}

static/css/main.css

@@ -490,6 +490,10 @@ section.main .container.f04 .content .detail {
     margin-bottom: 30px;
   }
 }
+section.main .container .content .groupby {
+  margin-top: 1em;
+  padding-left: 0.5em;
+}
 section.main .container .content .post-item {
   display: -webkit-flex;
   display: -moz-flex;