Blur checkbox on disabled. Fixes issues with shadow roots

Author: robdodson

elements/howto-checkbox/howto-checkbox.js

@@ -182,8 +182,7 @@
  this.removeAttribute('tabindex');
  // If the focus is currently on this element, unfocus it by
  // calling the `HTMLElement.blur()` method.
- if (document.activeElement === this)
- this.blur();
+ this.blur();
  } else {
  this.setAttribute('tabindex', '0');
  }