Check Dark/Light-Mode of UI

[casaout]

• is the experience sampling also available in dark mode? (created separate issue Dark mode for experience sampling #308)

• let's briefly check all windows in light mode

• on Malte's computer, the onboarding window on the second page looked off
  

• On Windows, the titles in the onboarding, about and export screens are a bit too light-gray:
  

• in light mode, the bullets of pagination are a bit off:
  

[SRichner]

[SRichner]

@casaout I updated all screens except for the experience sampling (dark mode)

[casaout]

@casaout I updated all screens except for the experience sampling (dark mode)

looks awesome, thank you!

For the dark mode, let's create an issue for the future :)