Focus Visible

Understanding WCAG2.0

Depending on elements and browsers, focus may not be visualized by default even if focus is received. It is a good idea to grant outline explicitly by CSS.

Principle Operable User interface components and navigation must be operable.
Guideline Navigable Provide ways to help users navigate, find content, and determine where they are.
Criterion Focus Visible
(2.4.7 AA)
Every user interface capable of operating the keyboard has an operation mode in which the focus indicator can be seen.

URL of Techniques for WCAG 2.0