dick/src/public/js/theme/theme-set.js

if (
    localStorage.getItem('color-theme') === 'dark' ||
    (!('color-theme' in localStorage) &&
      window.matchMedia('(prefers-color-scheme: dark)').matches)
  ) {
    document.documentElement.classList.add('dark');
  } else {
    document.documentElement.classList.remove('dark');
  }