flowbite-beardedtek.com/src/dark-mode.js

const themeToggleDarkIcon = document.getElementById('themeToggleDarkIcon');
const themeToggleLightIcon = document.getElementById('themeToggleLightIcon');

if (themeToggleDarkIcon && themeToggleLightIcon) {
    // Change the icons inside the button based on previous settings
    if (localStorage.getItem('color-theme') === 'dark' || (!('color-theme' in localStorage) && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
        themeToggleLightIcon.classList.remove('hidden');
    } else {
        themeToggleDarkIcon.classList.remove('hidden');
    }
}

const themeToggleBtn = document.getElementById('themeToggle');

let event = new Event('dark-mode');

if (themeToggleBtn) {

    themeToggleBtn.addEventListener('click', function() {

        // toggle icons
        themeToggleDarkIcon.classList.toggle('hidden');
        themeToggleLightIcon.classList.toggle('hidden');

        // if set via local storage previously
        if (localStorage.getItem('color-theme')) {
            if (localStorage.getItem('color-theme') === 'light') {
                document.documentElement.classList.add('dark');
                localStorage.setItem('color-theme', 'dark');
            } else {
                document.documentElement.classList.remove('dark');
                localStorage.setItem('color-theme', 'light');
            }

        // if NOT set via local storage previously
        } else {
            if (document.documentElement.classList.contains('dark')) {
                document.documentElement.classList.remove('dark');
                localStorage.setItem('color-theme', 'light');
            } else {
                document.documentElement.classList.add('dark');
                localStorage.setItem('color-theme', 'dark');
            }
        }

        document.dispatchEvent(event);
        
    });

}