_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">
  {%- seo -%}
  <link rel="stylesheet" href="{{ "/assets/css/style.css" | relative_url }}">
  {%- feed_meta -%}
  {%- if jekyll.environment == 'production' and site.google_analytics -%}
    {%- include google-analytics.html -%}
  {%- endif -%}

  {%- include custom-head.html -%}

  <!-- for mathjax -->
  <!-- <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script> -->
  <script type="text/javascript" async src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.3/MathJax.js?config=TeX-MML-AM_CHTML">
    MathJax.Hub.Config({
        tex2jax: {
            inlineMath: [["$", "$"]], //["\\(", "\\)"]],
            displayMath: [["$$", "$$"]], //["\\[", "\\]"]],
            processEscapes: true
        }
    });
    </script>
</head>