/* Theme chrome only: things that belong to the block theme's wrappers, not to the
   portable CRP pattern stylesheet.

   The header pattern is already position:sticky, but a sticky element can only move
   inside its own parent's box, and the block theme wraps every template part in a
   <header class="wp-block-template-part"> that is exactly as tall as the header. So
   the wrapper is what has to stick. */
header.wp-block-template-part{
  position:sticky;
  top:0;
  z-index:40;
}