Hey @tomayac , thank you for this custom element! I've started using it on a remake on my site and I really like it, it's been fun and easy to use! 🎉

I'm just wondering if there's a way to change the size of the icons? I see that there are CSS custom properties to change the font size of the labels, but I couldn't find one for the icons (please correct me if I'm wrong, I might have just missed it 😅 ).

I see from dark-mode-toggle.js#L127-130 that the icons have a size of 1rem, maybe a --dark-mode-toggle-icon-size custom property to customize this value?

Thanks! 😄

Since 5.3 Bootstrap is supporting color mode by a data attribute:
https://getbootstrap.com/docs/5.3/customize/color-modes/
It is a bit clumsy to integrate with this web component at the moment, ideally we can supply a query selector to this component to indicate the data-bs-theme value of the element(s) we would like to keep in sync with the toggle state, while default to the html tag so all elements will be included.

Can this be improved so that's there's no flash? I was considering your script because is similar to the way I implemented it on my site that is with a class that overrides custom styles but I have this very same problem which is kind of annoying for users in particular for dark mode as it blinds you for a sec. I forgot to mention: tested this on the demo site with remember preference on.

Currently terser is configured to minify all properties, and ends up even minifying access to attribute reflections.

For example:

is currently minified to

        (this.g = e.detail.g), (this.p.checked = this.g);

so it ends up accessing invalid properties, and same in other places.

Hey,

I've pretty much copied the examples and put the dark-mode-toggle markup into my code but I see absolutely no output. The element has no width or height or anything. Any ideas where I may be going wrong?

When using custom PNGs for the light/dark, I'm seeing a brief flash of the icon when the mouse hovers over the icon and when moving off of the icon. Using the OOTB icons this doesn't happen.

dark-mode-toggle {
  position: absolute;
  top: 0.5rem;
  right: 1rem;
  --dark-mode-toggle-light-icon: url(/assets/moon.png);
  --dark-mode-toggle-dark-icon: url(/assets/sun.png);
  --dark-mode-toggle-icon-size: 2rem;
  --dark-mode-toggle-icon-filter: invert(100%);
  transform:translate3d(0, 0, 0);
}

Not sure why this would be happening with custom PNGs.

When running the Chrome lighthouse, I am getting the following accessibility issue:

Could you please easer hard code an aria-label value or pass it down as a property?

Is there any way (currently) or are there any plans on adding a system theme option that would just reflect the system and not override it? Or do I have to somehow make a custom one that clears the localStorage?

When dark mode is active, when I refresh the page, it loads "LIGHT" first and then goes into dark mode. how can i fix this. If dark is selected, install dark.
it seems a little silly to start "light" first and switch to darkness immediately. I wonder if there is an error in my codes. I'm waiting for your help
you understand what I want to say from the video.
video

<meta name="color-scheme" content="dark light"/>
<meta name="theme-color" content="rgb(174, 129, 7)"/>
<link rel="icon" content="">
<link rel="stylesheet" href="'dark-mode/styles/light.css'" media="(prefers-color-scheme: light)">
<link rel="stylesheet" href="'dark-mode/styles/dark.css'" media="(prefers-color-scheme: dark)">
<link rel="stylesheet" href="'dark-mode/styles/common.css'">
<script type="module" src="'dark-mode/scripts/dark-mode-toggle.mjs'"></script>
<script type="module" src="'dark-mode/scripts/dark-mode-toggle-playground.mjs'"></script>
script
    if (window.matchMedia('(prefers-color-scheme)').media === 'not all') {
        document.documentElement.style.display = 'none';
        document.head.insertAdjacentHTML(
            'beforeend',
            '<link rel="stylesheet" href="dark-mode/styles/light.css" onload="document.documentElement.style.display = ``">'
        );
    }
</script>
<aside><dark-mode-toggle id="dark-mode-toggle-2" permanent></dark-mode-toggle></aside>

@tomayac
Hello! It would be cool if we could use Unicode emojis (☀🌙) instead of images for icons. Thank you in advance!

Tool used AXE https://chrome.google.com/webstore/detail/axe-devtools-web-accessib/lhdoppojpmngadmnindnejefpokejbdd

Steps to reproduce

1. Install AXE devtools extension in Chrome
2. Go to https://v8.dev/
3. Inside inspect Run Scan Page
   No errors Found
4. Now change toggle Dark/Light Theme Once
5. Rerun The Scan
6. Error " Form Elements Must Have Label"

Element Location:
dark-mode-toggle,#p

To solve this problem, you need to fix the following:
Form element has explicit that is hidden

Could it be possible to add the option to set SVG icons for light and dark icon toogle?

Hello, could you tell me how can I implement saving light/dark mode on my site like here (https://v8.dev/) without "Remember" checkbox? Adding "permanent" parameter doesn't help. Though this parameter is set in this website code and theme is saved without the checkbox.

When not setting a legend on the component there is still a right margin relative to the icon, see the following screenshot:

When no legends are set should not the icon be centred with no extra unnecessary margin?

EDIT: Also, why is the fieldset so wide compared to the icon, could we make the fieldset the same area than the icon or add a CSS vars to customise the fieldset? My goal here would be to set the width and height of the fieldset to 32px to match the other icons contained within mwc-button-icon.

First off, this is dope. Thank you.

I have a question about smooth transitions. I'm not a very experienced front-end developer, I'm a photographer trying to build my own stuff to avoid hosting fees while times are tough, and using the spare time to learn some html/css/js.

I stumbled across this on web.dev when trying how to get a theme for a static site generator to default the OS light/dark but remember overwritten user controls.

In that article, you have..
`body {
--duration: 0.5s;
--timing: ease;

color: var(--color);
background-color: var(--background-color);

transition:
color var(--duration) var(--timing),
background-color var(--duration) var(--timing);
}`
But there is no mention of it in the github version. With it still applied, the page blips from light to dark when the mode is permanent. I was curious what I need to look at specifically to fix that.

I noticed that if the person is in light mode and switches to dark mode and refreshes the page it continues in dark mode, now if the person is in dark mode and switches to light and refreshes the page it does not work page back for dark.

I use a select button

Can you help me?

// Get current theme
var theme = localStorage.getItem( 'theme' );
// Set defaults if theme is not defined.
if ( ! theme ) {
  localStorage.setItem( 'theme', 'light' );
  theme = 'light';
}
// Add theme to the body.
document.body.classList.add( theme );

// Handle onClick events
document.getElementById( 'theme-toggle' ).addEventListener( 'click', () => {
  // Cleanup classes from body.
  document.body.classList.remove( 'light' );
  document.body.classList.remove( 'dark' );
  // Change the theme.
  theme = ( theme === 'light' ) ? 'dark' : 'light';
  // Save the theme.
  localStorage.setItem( 'theme', theme );
  // Apply the theme.
  document.body.classList.add( theme );
});

if (window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches) {
	document.body.classList.remove( 'light' );
	document.body.classList.remove( 'dark' );
    var theme = 'dark';
	localStorage.setItem( 'theme', theme );
	document.body.classList.add( theme );
}
window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', event => {
	document.body.classList.remove( 'light' );
	document.body.classList.remove( 'dark' );
    var newColorScheme = event.matches ? "dark" : "light";
	localStorage.setItem( 'theme', newColorScheme );
	document.body.classList.add( newColorScheme );
});

Thanks for making this handy tool. It's really easy to just plug in and get working.

The icon needs a bit of bottom margin so that it is horizontally aligned with the label text:

The margin on label::before should be something like 0 .5rem .16rem 0, not 0 .5rem 0 0.

Alternatively, I think there's a way to put both elements in a flex container and align-content: center.

I can't override it myself since it is in a shadow dom.

Hi, well its been interesting to learn about Shadow CSS and ::parts but how can I style :: before and ::after using parts? It seems is not possible to target both at the same time. In my case I need to set different values for icons in the select button/form for width and height so it seems current variables are not enough. Maybe the code related to the toggle/switch could be further simplified.

Consider setting the attachShadow mode to open instead of closed so the internal dark-mode-toggle elements are accessible from outside the root, benefiting hacking into the functionality:

Currently if CSP (content security policy) does not already include unsafe-inline, client browser will refuse to load inline styles from this web component.

Due to the way this project is built it is not very easy for developers to get around this limitation.

I've been using this on all my websites for about a year now, and I appreciate that it's been working great. However, I just found out that the "permanent" toggle seems to have stopped working even though it's set to true. It keeps reverting to the default system theme.

I'm using via this CDN: https://googlechromelabs.github.io/dark-mode-toggle/src/dark-mode-toggle.mjs

I've tried on different browsers just to be sure it's not a browser issue.

It is somewhat weird that the png files are loading when I ran locally but were unable to load properly after committing the code to Github and ran using Github pages. (I am able to use the button but it is transparent🤷‍♂️.)
I am unable to figure out what is happening?

Link to Source Code

Local The moon png in the navigation bar

Github Pages

Code Snippets:
CSS

HTML

HEAD

Is there a reason to do UMD style at all? A module defined a scope, so you don't need a function scope to keep from accidentally creating globals. If you did, you could just use a block {} anyway.

Also, both the source file and dist file have .mjs extensions even though neither has an import or export. Is there a reason to check-in the minified file? It can be published to npm and available via unpkg.com without being checked in.

hi i wanted to download the source code and run it on localhost but unfortunately i get this error every time. what's the problem ? how can i solve?

no changes have been made to the file I get this error even when I want to use the demos

Failed to load module script: The server responded with a non-JavaScript MIME type of "". Strict MIME type checking is enforced for module scripts per HTML spec.

Hi GoogleChromeLabs,

I am no expert in web dev or web components, but in my current project when using the dark-mode-toggle, lit-plugin is throwing the following warning message:

Unknown tag <dark-mode-toggle>.
  Check that you've imported the element, and that it's declared on the HTMLElementTagNameMap. If it can't be imported, consider adding it to the 'globalTags' plugin configuration or disabling the 'no-unknown-tag' rule.lit-plugin(no-unknown-tag-name)(2322)

Is there anything you could do to fix the above?

Kind regards,
Alex

The GitHub Page is dead: https://googlechromelabs.github.io/dark-mode-toggle/

The buttons for changing from light to dark themes have disappeared on the site.

I added to my page so that the browser would draw dark scrollbars and other native widgets in dark mode. When I have the browser in dark mode and use the dark-mode-toggle switch to change my website to light mode, the widgets stay in dark mode. And vice versa... with browser in light mode and website toggled to dark mode, browser continues using light widgets. Is there any way to also toggle the meta tag so that native widgets follow the current theme? Not sure if it's possible but thought I would ask. Light widgets look OK in dark mode, but dark widgets look bad in light mode, so for now I removed the meta line to force light widgets.

we've experimented with your AMP variation. our planned site heavily uses SVG (rather than PNG/JPG). the dark-mode 'bleeds' thru the SVGs. we have a sample to share if you would like to see this use case. we would be willing to change our approach to using SVG linearGradient and radialGradient to work with dark-mode-toggle, but are uncertain how to do so. let me know if you are willing to collaborate with us on supporting SVGs and dark-mode-toggle.
/jay gray

I am a junior Dev and While implementing dark-mode-toggle and my other study from the below Google article I came across
aria-label="auto" aria-live="polite" for theme component.

https://web.dev/building-a-theme-switch-component/

In this, we keep the aria-label auto by default and change it to "light" or "dark" based on our toggle switch.
Also aria-live="polite" seems to add up.

If possible kindly have a look at these enhancements if deemed appropriate.

I built practically the same system for a site i'm working on but I actually really like some of the ideas you have put in here. My issue is that my dark/light styling is controlled via a high-level class. Could this be tweaked to allow a top-level class to be used rather than multiple stylesheets?

Thanks

Is there a way to style the toggle version like this: https://www.cssscript.com/realistic-ios-switch-pure-css/

Thanks.

I have my toggle set up as a toggle and the permanent attribute set. The icon I am using has a 1x1 aspect but I get some random margin on the right and bottom so the width doesn't match the height?

How can I remove these margins?

Also a way to be able to remove or alter the style of the focus styles would be useful.

This even happens on the demo site. https://googlechromelabs.github.io/dark-mode-toggle/demo/index.html

Tested on both Chrome and Firefox.

System must be configured to prefer dark, then light theme must be toggled on and remembered in the site. On page change or refresh, sometimes you'll get a frame or two where the dark theme is rendered first, then it flips over to the light theme as expected. With the demo site, because there's a transition enabled, you get the dark theme fading back into the light theme.

Hopefully a workaround is found for this!

Hi,

A DOMException error occurs when <dark-mode-toggle> is used in React apps.

Failed to construct 'CustomElement': The result must not have attributes

I think it occurs when document.createElement has been called.

The error would be solved if the DOM related tasks move from constructor to connectedCallback, but I am not sure this is an appropriate change for dark-mode-toggle.

The minification of template strings with terser currently is suboptimal, the problem being strings with repeated spaces and line breaks ending up in the minified code (excerpt):

`\n<style>\n*,\n::before,\n::after {\n  box-sizing: border-box;\n}\n\n:host {\n  […]`

This is most probably me holding terser wrong. Essentially I'm looking for something like babel-plugin-minify-template-strings, but for terser. Help wanted.

CC: @RReverser @mathiasbynens

Hi,

Firstly, great post at web.dev + good job with the element.

Just running into a wee issue. We have the following HTML,

<dark-mode-toggle appearance="toggle" permanent dark="Dark Theme" light="Light Theme"></dark-mode-toggle>

When the user toggles the color scheme, either via OS or via Chrome dev tools, the permanent setting is lost. Not sure if I got something wrong or I missed some detail or is this behaviour expected?

Example scenario: User OS theme set to dark. User visits website, dark theme loads by default. User changes website setting to light. User then changes OS them from dark to light and back to dark. The website switches to dark theme.

Also, is it possible to remove the outline in CSS (example would be handy), or even better add a ripple effect? Our website uses mdc-web-components. An example with a material text button as toggle would be super handy.

Cheers.

I have followed and read your tutorial at https://web.dev/prefers-color-scheme/ with great interest. It is a really nice tutorial for newbie like me, so many thanks for that.

Also, I decided to go the lazy/easy route and simply use your component rather than implementing all the logic behind for the theme switch.

My application is based on material web components - https://github.com/material-components/material-components-web-components - and style wise it does not really blend in, see the following screenshot:

As you can see my language button got a ripple around it, it is in fact a button when your component is just an icon, you can also see that the size is different, I have tried to see if I could wrap your component around a mwc-icon-button but I did not manage to get it to work.

This is the code that I have so far:

    <mwc-top-app-bar-fixed
            @MDCTopAppBar:nav=${() => (this.drawer.open = !this.drawer.open)}
          >
            <mwc-icon-button
              slot="navigationIcon"
              icon="menu"
              id="hamburger"
            ></mwc-icon-button>
            <h3 slot="title">Evil Corp</h3>
            <mwc-icon-button
              slot="actionItems"
              icon="languages"
            ></mwc-icon-button>
            <dark-mode-toggle
              slot="actionItems"
              appearance="toggle"
              permanent
            ></dark-mode-toggle>
            <!-- <mwc-icon-button-toggle
              onIcon="nights_stay"
              offIcon="wb_sunny"
              slot="actionItems"
            ></mwc-icon-button-toggle> -->
            <div class="navbar">
              <nav class="flex-container">
                <my-menu class="navbar-nav"></my-menu>
              </nav>
              <mwc-linear-progress></mwc-linear-progress>
            </div>
      </mwc-top-app-bar-fixed>

Also,I have notice that when my preferred theme is dark and I set the component to remember the choice when I visit the page again - refresh the page - it transition from dark theme to white theme, is this a know issue?

Hey,

I find that the remember feature doesn't seem to work for me. I load the site with my OS appearance set to light, the site shows in light, I then toggle to dark which the dark-mode-toggle and click remember. I see the local storage key getting set. I refresh the page and it shows in light, the local storage key also switched the light. Any ideas?

Also, once the above is working, what does it do if you switch the OS mode to be equal to the permanent setting, does this remove the local storage key as they will match and are no longer required? This would be a cool feature to have.

Great project overall, its a nice inspiration!

All solutions I discovered on the web with a permenent switch and also my own custom code suffer from a flash of the wrong styles at some point before the styles accoring to localStorage setting is applied. This happens in latest Chrome, but not in Desktop and Mobile Safari.

your regular demo does (on page reload) and v8.dev also, only your barebones demo seems fast enough

is it just not possible to avoid a flash (e.g. white background flash before dark background gets applied) without blocking the rendering or hiding the page or do have a suggestion?

Hello @tomayac,

In old browsers like Firefox 52, there is no support for Custom Elements. I'm using Webpack with Babel and I can't find a plugin to support Custom Elements. So i suggest you to do nothing if customElements is not defined.

// Do nothing if `customElements` does not exist. 
if (!window.customElements) return;

Thank you in advance !

Thanks for this awesome little widget, I've looked at quite a few dark mode toggles and I like the "switch" version of this one the most so far!

I would like to use it as a React component, so I'd like to ask if submitting such an abstraction layer over the current web component would be accepted here as a PR, or in case not, whether you'd be happy with me creating a separate wrapper package for it?

(I'd also like to include slider.css, moon.svg and sun.svg, but they aren't accessible from simply linking this package as a dependency, so in that case I would copy them and do my best to annotate them properly according to the Apache-2.0 license of this repo.)

DevTools supports emulating prefers-color-scheme. It would be great if dark-mode-toggle could play nice with this functionality. Some discussion: v8/v8.dev#254 (comment) + the workaround @RReverser used to make this work for v8.dev: v8/v8.dev@8ab0b70