I'm not familiar with that site, but it sounds like your browser may be enabling dark theme. This typically tries to follow your OS settings but isn't always perfect. What browser are you using and can you search to see if there are results for disabling dark mode in that browser?

The better fix is to try to use types that represent those units or data types (e.g. duration instead of ms). Makes it harder to accidentally use the wrong units and documents the code / intent better.