Improve contrast of doc's light version

[kakawait]

In light mode the doc snippet code contrast has low ration that lead to be hard to read even more for colorblind people or other disease.

And lighthouse confirmed

Personally I don't have any eyes disease but even reading the doc in late night was a bit tiring. (A bit too late in night to find out the switch button on topbar to switch to dark, then was perfect in dark mode).