mediarepo/_includes/previous-next_has-categories.html

<!-- Use if you want to show previous and next for posts within a category. -->
{% if page.categories %}
  {% assign category = page.categories[0] %}
  {% assign posts = site.categories[category] %}
  {% for post in posts %}
    {% if post.url == page.url %}
      {% assign post_index0 = forloop.index0 %}
      {% assign post_index1 = forloop.index %}
    {% endif %}
  {% endfor %}
  {% for post in posts %}
    {% if post_index0 == forloop.index %}
      {% assign next_post = post %}
    {% endif %}
    {% if post_index1 == forloop.index0 %}
      {% assign prev_post = post %}
    {% endif %}
  {% endfor %}
{% endif %}
{% assign user_url = site.url | append: site.baseurl %}
{% assign full_base_url = user_url | default: site.github.url %}
{% if prev_post %}
<div class="col-4 sm-width-full left mr-lg-4 mt-3">
  <a class="no-underline border-top-thin py-1 block" href="{{ prev_post.url | prepend: full_base_url }}">
    <span class="h5 bold text-accent">Previous</span>
    <p class="bold h3 link-primary mb-1">{{ prev_post.title }}</p>
    <p>{{ page.previous.content | strip_html | truncatewords:20 }}</p>
  </a>
</div>
{% endif %}
{% if next_post %}
<div class="col-4 sm-width-full left mt-3">
  <a class="no-underline border-top-thin py-1 block" href="{{ next_post.url | prepend: full_base_url }}">
    <span class="h5 bold text-accent">Next</span>
    <p class="bold h3 link-primary mb-1">{{ next_post.title }}</p>
    <p>{{ page.next.content | strip_html | truncatewords:20 }}</p>
  </a>
</div>
{% endif %}