:javascript
  function setDarkBeforeRender() {
    const localScheme = localStorage.getItem('scheme')
    if (localScheme == 'dark' || (localScheme == 'system' && window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
      document.documentElement.setAttribute('data-fr-theme', 'dark');
    }
  }
  setDarkBeforeRender();