Why does my do-nothing subtheme break the parent theme? I'm trying to get started with sub theming in Drupal 8. I followed the example from the Drupal documentation and created what I thought was supposed to be an unmodified inherited copy of the Bartik theme, but the main navigation menu is changed per the below screenshots. My code is as follows, identical to the tutorial other than Bartik as the base theme.

What am I missing here? Why am I not starting with an identical layout to the Bartik theme?

info.yml:

name: wilmettewatch
type: theme
description: Wilmette Watch's theme based off Bartik for now
core: 8.x
# Defines the base theme
base theme: bartik
# Defines libraries group in which we can add css/js.
libraries:
  - wilmettewatch/global-styling
# Regions
regions:
  header: Header
  featured: Featured
  content: Content
  sidebar_first: First sidebar
  sidebar_second: Second sidebar
  footer: Footer


libraries.yml:

global-styling:
  css:
    component:
      css/style.css: {}


Bartik Theme:



My Sub Theme:
The sub theme is fine. Sometimes when you activate a sub theme, you may need to recreate some or all of the block layout. In this case, the primary menu got placed in the header, where it gets a different layout. 

Just make note of the block layout in the Bartik theme and duplicate it in the sub theme.