_includes/head.html

<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1">

  <link rel="stylesheet" href="{{ "/assets/css/main.css" | relative_url }}">

  {% if page.custom_css %}
    {% for stylesheet in page.custom_css %}
    <link rel="stylesheet" href="/assets/css/{{ stylesheet }}.css" media="screen" type="text/css">
    {% endfor %}
  {% endif %}

  <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 %}

  <!-- HTML5 shim and Respond.js for IE8 support of HTML5 elements and media queries -->
  <!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
  <!--[if lt IE 9]>
    <script src="https://oss.maxcdn.com/html5shiv/3.7.3/html5shiv.min.js"></script>
    <script src="https://oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
  <![endif]-->

  {% if site.gems contains "jekyll-seo-tag" %}
    {% include seo-tag.html %}
  {% else %}
    <title>{% if page.title %}{{ page.title | escape }} | {% endif %}{{ site.title | escape }}</title>
  {% endif %}

</head>