Improve accessibility by adding light / dark mode and increasing text size possibly variables.scss issue

[lschmid83]

I would like to improve the accessibility of the website for people with poor eyesight or disabilities. I did begin to implement this in the variables.scss file for easily setting the color of different components. It needs some more work and the first thing to do would be to add a light and dark mode then possibly make it easy to increase the font size.