This page chose templates/shell.html. The header and footer
around it are blocks the layout embeds with
x-block, and this page sits in the layout's
<cnc-block name="main">
region. The header's buttons move main, and the next page lands
in the same region.
<!-- templates/shell.html -->
<header><div x-block="'/layouts/shell-header'"></div></header>
<cnc-block name="main">
<slot></slot> <!-- the page lands here -->
</cnc-block>
<footer><div x-block="'/layouts/shell-footer'"></div></footer>