Open the HTML layout configuration file:
source +--- layout +--- html.json
Add a new entry with the block template path:
{ ... "banner": "template/block/banner.html" ... }
Create the new block template file with the HTML content:
source +--- template +--- block +--- banner.html
<div id="banner">
Welcome!
</div>
Add the new block in the page template:
source +--- template +--- default.html
<!-- ... -->
<main>
\{% banner %\}
<!-- ... -->
</main>
<!-- ... -->