fix: #249 change accent color to lighter for better contrast in dark mode

[Koziolek]

Based on contrast color calculator, I change --accent-color variable to achieve passing minimal requirements for WCAG AAA for normal text and WCAG AA for graphical objects.

For combination --accent-color on --bg-even-row contrast ratio is 7:1 For combination --accent-color on --bg-odd-row contrast ratio is 9.14:1

That pass WCAG requirements.