Example template

custom.twig

{% extends 'base.twig' %}
{% block title %}Custom Page Title{% endblock %}
{% block css %}
  {{ parent() }}
  <link rel="stylesheet" type="text/css" href="/my/custom/file.css">
{% endblock %}
{% block content %}
  all content goes in here
{% endblock %}
{% block js %}
  {{ parent() }}
  <script src="/custom/file.js"></script>
{% endblock %}