Bad contrast on trial balance chart/text

[jakobhellermann]

In light mode, the contrast is ok but it feels like the text could be a bit darker.

In dark mode, the text is really unreadable.

The styling comes from

fava/frontend/css/charts.css

Line 3 in e1ea345

fill: var(--text-color-lightest);

which is defined here

fava/frontend/css/style.css

Line 38 in e1ea345

--text-color-lightest: light-dark(hsl(0deg 0% 40%), hsl(0deg 0% 65%));