Starting from WordPress 5.2 a new function is added – `wp_body_open()` – that is used to trigger a `wp_body_open` action. The function should be placed inside of the <body> tag immediately after it is opened.
* Add the header and footer styles to `style-editor.scss`.
* Add the `.entry-content` class to the header and footer when in FSE context.
* Add some styles overrides for the FSE blocks in the header template.
* Adjust the Template block paddings.
* Stop `display: flex;` the footer to avoid incorrect positioning of the footer blocks.
* Add a responsive version of the main navigation, as featured in Varia and most Varia-based themes.