Did you end up explaining how to highlight 'contact' when that page is selected?

Here's how I did mine:

In main.twig:

<a href={{ siteUrl('/contact') }} {% block contact_act %}{% endblock contact_act %}>Contact</a>

In contact.twig:

{% block contact_act %}class="selected"{% endblock contact_act %}

Do this for each link (named accordingly).

It is not that tricky actually. All you have to do is overwrite data in contact page to make it highlighted in the nav menu. For sure there are few ways of doing that but i will explain you method I used for title - same will work for you. We start with title inside main.twig looking like this

<title>{%  block title %}Your title{%  endblock title %}</title>

And when creating contact.twig you can add this line to change title to something else

{%  block title %}Title saying something else{%  endblock title %}

Make highlighted item in its .twig file not the global one for template (main.twig used in video) and change it when needed.

I used {% block nav %} in main.twig around the nav. Then used the below to override it in contact.twig

 {% block nav %}
      <a href="http://localhost/composer_example">About</a>
      <a href="contact" class="selected">Contact</a>
 {% endblock nav %}