How to add a button to the titlebar of an admin page?

Hello Grav Community,

can somebody please briefly list the steps that are required to add some buttons to an admin page?
I've added a new page and menu to the admin plugin (similar as it's done in the comments plugin), but placing the following in the templates .html.yaml file (which has been copied from the comments plugin) doesn't display anything, so I guess something is missing:

{% block titlebar %}
    <div class="button-bar">
        <a class="button" href="{{ base_url_relative }}/myplugin"><i class="fa fa-arrow-left"></i> {{ "MYPLUGIN.BTN_NEW"|tu }}</a>
        <button class="button" type="submit" name="task" value="save" form="blueprints"><i class="fa fa-check"></i> {{ "MYPLUGIN.BTN_SAVE"|tu }}</button>
    </div>
    <h1><i class="fa fa-fw fa-plug"></i> {{ "MYPLUGIN.TITLE"|tu }}: {{ plugin.name|e }}</h1>
{% endblock %}

Any advise is welcome,
Thank you.

*.html.twig you mean, right?

Yes, that's where it was placed, but nothing showed up. All out of a sudden it worked - unfortunately I have no clue what went wrong. Anyway, thank you for your support.

Maybe you forgot to clear the cache after creating or modyfing your script. I recommend to completely turn off all cache functions during development.

Yes, it's most likely related to it. Well, I did clear the cache various times, but finally gave up on it. The next day, after installing the update to 1.0.9 (whole system was rebooted in between) the buttons showed up.