I love 18F! A few months back they published a set of web design standard [0] that I really liked. Accessibility is among their top concerns, so it's legible in all devices and there's a lot of contrast.
I used their color suggestions for my blog [1] (still haven't updating syntax highlighting, terribly sorry about that). The two things I changed were typography sizes and fonts. I decided it would be best to use preinstalled fonts instead of loading a third-party font. I don't think third-party fonts justify slower load times for a static website like my blog. But overall, I really like their color scheme, as it's very comfortable to read on any screen.
I used their color suggestions for my blog [1] (still haven't updating syntax highlighting, terribly sorry about that). The two things I changed were typography sizes and fonts. I decided it would be best to use preinstalled fonts instead of loading a third-party font. I don't think third-party fonts justify slower load times for a static website like my blog. But overall, I really like their color scheme, as it's very comfortable to read on any screen.
[0] https://standards.usa.gov/getting-started/
[1] https://blog.cesarandreu.com/