_includes/head.html

<head>

  <!-- Google Tag Manager -->
  <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
  new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
  j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
  'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
  })(window,document,'script','dataLayer','GTM-KJ4Q3WT');</script>
  <!-- End Google Tag Manager -->
    
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1">

  <title>{% if page.title %}{{ page.title | escape }}{% else %}{{ site.title | escape }}{% endif %}</title>
  <meta name="description" content="{{ page.excerpt | default: site.description | strip_html | normalize_whitespace | truncate: 160 | escape }}">

  <link rel="stylesheet" href="{{ "/assets/main.css" | relative_url }}">
  <link rel="canonical" href="{{ page.url | replace:'index.html','' | absolute_url }}">
  <link rel="alternate" type="application/rss+xml" title="{{ site.title | escape }}" href="{{ "/feed.xml" | relative_url }}">

  {% if jekyll.environment == 'production' and site.google_analytics %}
  {% include google-analytics.html %}
  {% endif %}

</head>