css-custom-properties.js

function toggleTheme() {
  const theme = window.localStorage.getItem("theme");

  if (theme === "light") {
    setTheme("#262b2f", "white", "🌝", "dark");
  } else {
    setTheme("white", "#262b2f", "🌚", "light");
  }
}

function setTheme(background, text, toggleText, theme) {
  document.body.style.setProperty("--background-color", background);
  document.body.style.setProperty("--text-color", text);
  document.getElementById("theme-btn").innerText = toggleText;
  window.localStorage.setItem("theme", theme);
}