Add a theme-color (#18976)

layouts/partials/head.html

@@ -12,6 +12,7 @@
 <meta charset="utf-8">
 <title>{{ if .Title }}{{ .Title }} - {{ end }}{{ site.Title }}</title>
 <meta name="viewport" content="width=device-width, initial-scale=1">
+<meta name="theme-color" content="#326ce5">
 <link rel="shortcut icon" type="image/png" href="{{ "images/favicon.png" | relURL }}">
 {{ partial "css.html" . }}
 <!-- Content for social media sharing previews -->