Buttons and links must keep enough contrast on hover and focus

The check reads a[href], button, [role="button"], [role="link"] and input buttons, skipping disabled, hidden and nearly transparent ones. It samples one element per style (tag, class, colors, font, page region), up to 60 per page, and freezes CSS transitions to read final colors.

After one real Tab press, so :focus-visible applies, each sample is read in its default state, then focused. Samples with text that are topmost at their center are also hovered with the mouse, until 10 seconds into the check.

Text is a finding when a hover or focus state with changed colors falls below 4.5:1, or 3:1 for large text (24 px, or 18.66 px bold). Colors are composited through ancestor backgrounds and opacity onto white; text over an image, video or other overlapping box is skipped. A focus outline or added box-shadow is a finding when the best one is below 3:1 against the adjacent background; the browser’s auto ring is not measured. Borders, underlines and background changes are not measured as focus indicators.