function setClassOnDocumentBody(darkMode) {
                  document.body.classList.add(darkMode ? classNameDark : classNameLight);
                  document.body.classList.remove(darkMode ? classNameLight : classNameDark);
                }
MEMO: inspired by https://web.dev/prefers-color-scheme/#activating-dark-mode-in-the-operating-system.
for now we take the approach https://github.com/GoogleChromeLabs/dark-mode-toggle#-using-a-css-class-that-you-toggle
as it's not supported in SSR environment.