试图在Symfony 3中包含一个标题块

I am totally new to this. I took as an example the body block.

This is my base.html.twig file content:

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8" />
        <title>{% block title %}Welcome!{% endblock %}</title>
        {% block stylesheets %}{% endblock %}
        <link rel="icon" type="image/x-icon" href="{{ asset('favicon.ico') }}" />
    </head>
    <body>
        {% block header %} {% endblock %}
        {% block body %}{% endblock %}
        {% block footer %}{% endblock %}
        {% block javascripts %}{% endblock %}
    </body>
</html>

and this is my header from app\Resources\views\header\header.html.twig content:

{% extends 'base.html.twig' %}
{% block header %}
Header HeaderHeaderHeaderHeader
{% endblock %}

But this is not working for some reason. Do i need to do smth more ? thx

[UPDATE]

I attached an image to see what i want to achieve: enter image description here

This is folder structure: enter image description here

[UPDATE]

The content of the index.html.twig file is:

{% extends 'base.html.twig' %}

{% block body %}
    <div id="wrapper">
        <div id="container">
          afdsfsdfsfasddf
        </div>
    </div>
{% endblock %}

{% block stylesheets %}
<style>
    body { background: #F5F5F5; font: 18px/1.5 sans-serif; }
</style>
{% endblock %}

I suggest you to do that:

base.html.twig

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8" />
        <title>{% block title %}Welcome!{% endblock %}</title>
        {% block stylesheets %}{% endblock %}
        <link rel="icon" type="image/x-icon" href="{{ asset('favicon.ico') }}" />
    </head>
    <body>
        {# header section #}
        <div>
             {% include ':header:header.html.twig' %}
             {% block header %} {% endblock %}
        </div>            

        {# body section #}
        <div>
             {% block body %}{% endblock %}
        </div>

        {% block footer %}{% endblock %}
        {% block javascripts %}{% endblock %}

    </body>
</html>

header.html.twig

Remove this section

{% extends 'base.html.twig' %}
{% block header %}
Header HeaderHeaderHeaderHeader
{% endblock %}

And make only the header content

index.html.twig

{% extends 'base.html.twig' %}

{% block body %}
    <div id="wrapper">
        <div id="container">
          afdsfsdfsfasddf
        </div>
    </div>
{% endblock %}

{% block stylesheets %}
<style>
    body { background: #F5F5F5; font: 18px/1.5 sans-serif; }
</style>
{% endblock %}