The contrast between the colours and the background must be sufficient for all items present (text, images, videos, etc.).
To test the contrast, you could use, for example, the Contrast Analyser tool for Windows and Mac OS, which you can download free at Contrast Analyser, disponible en libre téléchargement pour Windows et Mac OS.
According to this tool, the contrast ratio is considered as sufficient if it reaches the standard AA.
Alternative style guidelines do not necessarily push the contrast to the limits (for example, black on white, or white on black), but provide rules so that the association of colours is optimized satisfactorily.
in this example, alternative style guidelines that are sufficiently contrasted
can be activated from the button “Change the page contrast”.