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Easily add a ‘smart’ dark mode to any website or web app


ui, css, javascript

Today, let’s spice up our web project with a dark mode easter egg. To set up this feature in our project, we’ll need a few lines of CSS that will change the colors and background colors of elements on our site.

James Bond is based on real WWII spy, Dusan Popov.

A starry night sky - when the world is in dark mode

The most obvious way is to apply a CSS invert() filter to everything under dark mode conditions. In this case, we’re toggling a class of ‘dark-mode’ on the body element.

body.dark-mode {
    filter: invert(1);

We could just throw this in our stylesheet and call it good. But we’re not going to settle for that, are we? Let’s make this a ‘smart’ dark mode, to imitate a popular iOS feature. For the dark mode to be smart, it needs to ignore images, only inverting things like typography and background colors.

body.dark-mode {
    background: currentColor;

body.dark-mode h1,
body.dark-mode h2,
body.dark-mode h3,
body.dark-mode h4,
body.dark-mode h5,
body.dark-mode p,
body.dark-mode ul,
body.dark-mode ol,
body.dark-mode p img,
body.dark-mode ul img,
body.dark-mode ol img {
    filter: invert(1)

body.dark-mode ul h1,
body.dark-mode ul h2,
body.dark-mode ul h3,
body.dark-mode ul h4,
body.dark-mode ul h5,
body.dark-mode ul p,
body.dark-mode ol h1,
body.dark-mode ol h2,
body.dark-mode ol h3,
body.dark-mode ol h4,
body.dark-mode ol h5,
body.dark-mode ol p {
    filter: none


To make this work, we need two functions - one that checks if dark mode is enabled on page load, and another that toggles dark mode when an event happens. We can use JSON.parse() to ensure that the darkModeOn value gets returned as the boolean true, not the string “true” when we get it from local storage.

function checkDarkMode() {

    let darkModeOn = JSON.parse(localStorage.getItem('darkModeOn')) || false;
    if (darkModeOn) document.body.classList.add('dark-mode');


function toggleDarkMode() {

    // If dark mode is on, turn off, otherwise, turn on
    darkModeOn ? darkModeOn = false : darkModeOn = true;

    // Store setting in local storage
    localStorage.setItem('darkModeOn', darkModeOn);

    // Toggle dark mode class on the body


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