MediaWiki:Vector.js

$(document).ready(function() {
  var button = document.createElement("button");
  button.innerHTML = "Сменить тему";
  button.className = "theme-button";
  button.onclick = toggleTheme;

  var container = document.getElementById("p-personal");
  if (container) {
      container.parentNode.insertBefore(button, container);
  }

  var isLightTheme = localStorage.getItem("isLightTheme");
  if (isLightTheme === "true") {
      document.documentElement.classList.add('light');
  } else {
      document.documentElement.classList.remove('light');
  }
});

function toggleTheme() {
  var isLightTheme = document.documentElement.classList.toggle('light');
  localStorage.setItem("isLightTheme", isLightTheme);

  setTimeout(function() {
      if (isLightTheme) {
          document.documentElement.style.setProperty('--color-fg', '#252525');
          document.documentElement.style.setProperty('--color-bg', '#ffffff');
      } else {
          document.documentElement.style.setProperty('--color-fg', '#ffffff');
          document.documentElement.style.setProperty('--color-bg', '#252525');
      }
  }, 10);
}