This is a testharness.js-based test.
[FAIL] "::before::column" should be a valid selector
  Failed to execute 'querySelector' on 'Document': '::before::column' is not a valid selector.
[FAIL] "::before::column::scroll-marker" should be a valid selector
  Failed to execute 'querySelector' on 'Document': '::before::column::scroll-marker' is not a valid selector.
Harness: the test ran to completion.