Add site header template part

[seothemes]

After looking at the new collection of theme designs, I think we need to start planning for block based site headers.

Any navigation menus in this template part would automatically be added to the Mobile Menu.

The template part would need to be wrapped with the <header class="site-header"></header> markup to allow for transparent and sticky headers.

Having this template part would remove the need for Header Left and Header Right, but we would need to add After Header to allow for after header menus, as they are not included in sticky headers.

Example of a block based site header template part: