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WCAG: 1.4.3: Text elements must have sufficient color contrast against the background
All text elements must have sufficient contrast between text in the foreground and background colors behind it in accordance with WCAG 2 AA contrast ratio thresholds.
Some people with low vision experience low contrast, meaning that there aren't very many bright or dark areas. Everything tends to appear about the same brightness, which makes it hard to distinguish outlines, borders, edges, and details. Text that is too close in luminance (brightness) to the background can be hard to read.
There are nearly three times more individuals with low vision than those with total blindness. One in twelve people cannot see the average full spectrum of colors - about 8% of men and 0.4% of women in the US. A person with low vision or color blindness is unable to distinguish text against a background without sufficient contrast.
Color transparency and opacity is taken into account in the background.
Color transparency and opacity in the foreground is more difficult to detect and account for due to:
- 1:1 colors in foreground and background.
- CSS background gradients.
- Background colors in CSS pseudo-elements.
- Background colors created with CSS borders.
- Overlap by another element in the foreground - this sometimes comes up with tricky positioning.
- Elements moved outside the viewport via CSS.