Hi stephane-lavoisard,
When creating a template style, you can click Add new header block and put the following code to the block.
<!-- HEADER BLOCK -->
<header id="t4-header-wrap" class="t4-header w-100">
<div class="t4-header-inner">
<div class="row no-gutters d-flex align-content-center justify-content-between flex-nowrap">
<div class="col-auto t4-logo-header d-flex align-content-center col-xl-4">
<jdoc:include type="element" name="logo" />
</div>
<div class="t4-megamenu-wrap col-auto d-flex justify-content-end col-xl-8">
<div class="t4-navbar d-flex align-content-center">
<jdoc:include type="element" name="megamenu" />
</div>
<div class="t4-header-right d-flex">
<div class="head-search">
<jdoc:include type="modules" name="head-search" />
</div>
<jdoc:include type="element" name="offcanvas-toggle" />
<jdoc:include type="element" name="megamenu-toggle" />
</div>
</div>
</div>
</div>
</header>
<!-- // HEADER BLOCK -->
I have updated the header block in the template style ID 72.
