Accessibility checks
See whether text is readable as you style it, and choose what a publish does with accessibility problems.
Contrast as you style
With one text selected, its Text color shows its contrast with what the text sits on: the ratio, and whether it meets AA or AAA for its size. Large text (24 px and up, or 18.66 px and up in bold) needs 3:1, the rest 4.5:1. A text on a gradient, an image, a see-through colour, or with an outline gets no rating: its contrast depends on what's drawn under it.
Each publish is checked
Each publish checks the site's home page and its four most-linked pages for accessibility problems, and lists what it finds. Before you publish, the checks list text that is hard to read against its background, in dark mode too when the site has it.
Accessibility check… in the site menu chooses what a serious or critical problem does to a production publish: turn on Block publishing on serious problems to stop the publish and list what to fix; off, the site publishes and lists them as warnings. Staging always publishes, so you can check a fix there first.