People with low vision or dyslexia may override an author's set spacing to enable readability or increased reading speed. Increased spacing between lines, words, letters, and paragraphs has benefits for people who override author settings via user stylesheet, bookmarklet, extension, or application. Setting a fixed format (px, cm, mm, pt, pc) on letter-spacing, line-height or word-spacing may restrict the ability of these users to override the default setup of the page. If the line-height is defined in pixels but the font size is larger than the pixel value, lines of text will clash into each other. If letter or word spacing is defined in an absolute value larger text might have letters or words that are too close to each other. See WCAG 2.1, 1.4.12
How can I resolve this issue?
Instead of using fixed font measurements use relative font measurements instead such as em and % that adjust based on how the page is being viewed.
What topics do this checkpoint affect?
Accessibility (WCAG 2.1, 1.4.12)
Can you explain how this checkpoint works?
This checkpoint flags an issue when:
The CSS property letter-spacing: is using a fixed format (px, cm, mm, pt, pc)
The CSS property line-height: is using a fixed format (px, cm, mm, pt, pc)
The CSS property word-spacing: is using a fixed format (px, cm, mm, pt, pc)