themes: upgrade to Drupal 8, custom theme that does not use a referenced CSS file

I am updating a theme from Drupal 7 to Drupal 8. I am referring to .css files in mytheme.library.yml that don't seem to be entering the site.

I have searched online and even copied sample codes and replaced the names appropriately. However, I don't see any .css files being applied or referenced in the source code or Developer Tools.

If these files look correct, any address of what might be the cause will be appreciated. If it's permissions let me know what permissions it MUST be!

I've cleaned the cache hundreds of times, after each change, as well as using incognito mode, so I know it's not a site or browser caching issue.

Thank you.

Content of sites / all / themes / mytheme / mytheme.info.yml

name: MyTheme
type: theme
description: My theme.
core: 8.x
base theme: bootstrap
logo: logo.png

regions:

  navigation: 'Navigation'
  header: 'Top Bar'
  highlighted: 'Highlighted'
  help: 'Help'
  content: 'Content'
  sub_content: 'Sub-content'
  sidebar_first: 'Primary'
  sidebar_second: 'Secondary'
  footer: 'Footer'
  page_top: 'Page top'
  page_bottom: 'Page bottom'
  footer_firstcolumn: 'Footer first column'
  footer_secondcolumn: 'Footer second column'

libraries:
  - mytheme/global-assets

Content of sites / all / themes / mytheme / mytheme.library.yml

global-assets:
  version: VERSION
  css:
    theme:
      css/main.css: {}
      css/bootstrap.css: {}
  js:
    js/main.js: {}
    js/bootstrap.min.js: {}
    js/enquire.min.js: {}
    js/jquery.main.js: {}

Any help or direction would be appreciated.

Thank you