guideline: Navigable
Help users find their way and know where they are in the website.
2.4.11 Focus Not Obscured (Minimum)
The keyboard focus is not completely hidden by other content.
2.4.12 Focus Not Obscured (Enhanced)
The keyboard focus is fully visible at all times.
2.4.13 Focus Appearance
Focus indicators are at least 2px thick and have a 3:1 contrast ratio against adjacent colors.