CSS

• About theme change, just use CSS variable. I mean var() not the $ of Sass, because CSS variable not translate to hard code, it just var for itself

• Set var in the :root

:root {
  --primary: black;
  --second: white;
}

• After that combine body with some class and change the value of css variable

body.dark {
  --primary: white;
  --second: black;
}

JavaScript

• Hour (from 0 to 11), minute and second (0 to 59) take that and use scale function to map that range of number to circle degree (0 to 360) that way we can make the tick point to exact ratio

• scale function

function scaleRange(number, inMin, inMax, outMin, outMax) {
  return ((number - inMin) * (outMax - outMin)) / (inMax - inMin) + outMin;
}

Screenshot

Light Theme

Dark Theme

Live Site

URL: Link