How do I apply dark mode to all the website’s pages via localstorage?

The dark mode is being saved via local storage, but it’s not being applied to all the site’s pages automatically. How can I make sure that when I choose dark mode, it is applied to all pages of the website automatically? How do I apply what I’ve saved in localstorage?

let trilho = document.getElementById('trilho');
let body = document.querySelector('body');

// Check local storage for the user's theme preference
const theme = window.localStorage.getItem("theme");

// Set the initial theme based on localStorage
if (theme === "dark") {
    body.classList.add("dark");
    trilho.classList.add("dark"); // Ensure the button reflects dark mode
} else {
    trilho.classList.remove("dark"); // Ensure the button reflects light mode
}

// Add event listener to toggle dark mode
trilho.addEventListener('click', () => {
    trilho.classList.toggle('dark');
    body.classList.toggle('dark');

    // Update localStorage with the current theme
    if (body.classList.contains("dark")) {
        window.localStorage.setItem("theme", "dark");
        trilho.classList.add("dark"); // Dark mode button
    } else {
        window.localStorage.setItem("theme", "light");
        trilho.classList.remove("dark"); // Light mode button
    }
});