Light/Dark Theme Toggle with CSS and JavaScript

This JavaScript and CSS code snippet helps you to create light/dark theme toggle functionality for your website. It comes with a checkbox toggle button that switch between light and dark mode. The JavaScript function detects the checkbox checked property and add an attribute “data-theme” to the root of document with two possible values, “light” and “dark”. The CSS contains the styles for the dark and light mode in variables. So, when a user checked the checkbox, the dark mode will be activated.

How to Create Light/Dark Theme Toggle with CSS and JavaScript

1. First of all, create an input element with a unique id “switch” and define its name attribute with “theme” value. Similarly, create a label tag associated with it, wrap both elements into a div tag and define its class name “toggle-container”. You can place this toggle button anywhere in your HTML where you want to display a light/dark switch button.

<div class="container">
        <h1>Light / Dark Mode</h1>
        <div class="toggle-container">
            <input type="checkbox" id="switch" name="theme" /><label for="switch">Toggle</label>
        </div>

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    </div>

2. Now, add the following CSS styles to your project. You can modify the styles for the html selector according to your webpage.

html {
  height: 100%;
  font-family: "Montserrat";
  display: grid;
  align-items: center;
  justify-items: center;
  --bg: #FCFCFC;
  --bg-panel: #EBEBEB;
  --color-headings: #0077FF;
  --color-text: #333333;
}

html[data-theme=dark] {
  --bg: #333333;
  --bg-panel: #434343;
  --color-headings: #3694FF;
  --color-text: #B5B5B5;
}

body {
  background-color: var(--bg);
}

.container {
  background-color: var(--bg-panel);
  margin: 5em;
  padding: 5em;
  border-radius: 15px;
  display: grid;
  grid-template-columns: 80% auto;
  grid-template-rows: auto auto;
  grid-template-areas: "title switch" "content content";
}
.container h1 {
  margin: 0;
  color: var(--color-headings);
}
.container p {
  color: var(--color-text);
  grid-area: content;
  font-size: 1.1em;
  line-height: 1.8em;
  margin-top: 2em;
}

input[type=checkbox] {
  height: 0;
  width: 0;
  visibility: hidden;
}

label {
  cursor: pointer;
  text-indent: -9999px;
  width: 52px;
  height: 27px;
  background: grey;
  float: right;
  border-radius: 100px;
  position: relative;
}

label:after {
  content: "";
  position: absolute;
  top: 3px;
  left: 3px;
  width: 20px;
  height: 20px;
  background: #fff;
  border-radius: 90px;
  transition: 0.3s;
}

input:checked + label {
  background: var(--color-headings);
}

input:checked + label:after {
  left: calc(100% - 5px);
  transform: translateX(-100%);
}

label:active:after {
  width: 45px;
}

html.transition,
html.transition *,
html.transition *:before,
html.transition *:after {
  transition: all 750ms !important;
  transition-delay: 0 !important;
}

3. Finally, add the following JavaScript function before closing of the body tag.

var checkbox = document.querySelector('input[name=theme]');

        checkbox.addEventListener('change', function() {
            if(this.checked) {
                trans()
                document.documentElement.setAttribute('data-theme', 'dark')
            } else {
                trans()
                document.documentElement.setAttribute('data-theme', 'light')
            }
        })

        let trans = () => {
            document.documentElement.classList.add('transition');
            window.setTimeout(() => {
                document.documentElement.classList.remove('transition')
            }, 1000)
        }

That’s all! hopefully, you have successfully created light/dark theme toggle with CSS and JavaScript. If you have any questions or suggestions, feel free to comment below.

Asif Mughal

I code and create web elements for amazing people around the world. I like work with new people. New people new Experiences.
I truly enjoy what I’m doing, which makes me more passionate about web development and coding. I am always ready to do challenging tasks whether it is about creating a custom CMS from scratch or customizing an existing system.