zola/docs/templates/shortcodes/gallery.html

<div>
{% for asset in page.assets -%}
  {%- if asset is matching("[.](jpg|png)$") -%}
    {% set image = resize_image(path=asset, width=240, height=180) %}
    <a href="{{ get_url(path=asset) }}" target="_blank">
      <img src="{{ image.url }}" />
    </a>
  {%- endif %}
{%- endfor %}
</div>