documentation/extensions/odoo_theme/layout_templates/header.html

<div class="o_logo_wrapper">
      <a href="{{ pathto(master_doc) }}" class="o_logo">
          <img src="{{ pathto('_static/img/logos/odoo_logo.svg', 1) }}" height="20" alt="Odoo"/>
          <span>docs</span>
      </a>
</div>
{%- include "layout_templates/searchbox.html" %}
<div class="d-none d-lg-flex ms-auto">
    {%- include "layout_templates/language_switcher.html" %}
    {%- include "layout_templates/version_switcher.html" %}
    <a class="btn btn-primary fw_semibold" href="https://odoo.com/trial">{{ _('Try Odoo for FREE') }}</a>
</div>