How to override css prefers-color-scheme setting
I am implementing a dark mode, as macOS, Windows and iOS have all introduced dark modes.
There is a native option for Safari, Chrome, and Firefox, using the following CSS media rule:
@media (prefers-color-scheme: dark) {
body {
color:#fff;
background:#333333
}
This will automatically identify systems that are set to dark modes, and apply the enclosed CSS rules.
However; even though users may have their system set to dark mode, it may be the case that they prefer the light or default theme of a specific website. There is also the case of Microsoft Edge users which does not (yet) support @media (prefers-color-scheme. For the best user experience, I want to ensure that these users can toggle between dark and default modes for those cases.
Is there a method that this can be performed, possibly with HTML 5 or JavaScript? I'd include the code I have tried, but I haven't been able to find any information on implementing this whatsoever!
Solution 1:
I have determined an appropriate solution, it is as follows:
CSS will use variables and themes:
// root/default variables
:root {
--font-color: #000;
--link-color:#1C75B9;
--link-white-color:#fff;
--bg-color: rgb(243,243,243);
}
//dark theme
[data-theme="dark"] {
--font-color: #c1bfbd;
--link-color:#0a86da;
--link-white-color:#c1bfbd;
--bg-color: #333;
}
The variables are then called where necessary, for example:
//the redundancy is for backwards compatibility with browsers that do not support CSS variables.
body
{
color:#000;
color:var(--font-color);
background:rgb(243,243,243);
background:var(--bg-color);
}
JavaScript is used to identify which theme the user has set, or if they have over-ridden their OS theme, as well as to toggle between the two, this is included in the header prior to the output of the html <body>...</body>:
//determines if the user has a set theme
function detectColorScheme(){
var theme="light"; //default to light
//local storage is used to override OS theme settings
if(localStorage.getItem("theme")){
if(localStorage.getItem("theme") == "dark"){
var theme = "dark";
}
} else if(!window.matchMedia) {
//matchMedia method not supported
return false;
} else if(window.matchMedia("(prefers-color-scheme: dark)").matches) {
//OS theme setting detected as dark
var theme = "dark";
}
//dark theme preferred, set document with a `data-theme` attribute
if (theme=="dark") {
document.documentElement.setAttribute("data-theme", "dark");
}
}
detectColorScheme();
This javascript is used to toggle between the settings, it does not need to be included in the header of the page, but can be included wherever
//identify the toggle switch HTML element
const toggleSwitch = document.querySelector('#theme-switch input[type="checkbox"]');
//function that changes the theme, and sets a localStorage variable to track the theme between page loads
function switchTheme(e) {
if (e.target.checked) {
localStorage.setItem('theme', 'dark');
document.documentElement.setAttribute('data-theme', 'dark');
toggleSwitch.checked = true;
} else {
localStorage.setItem('theme', 'light');
document.documentElement.setAttribute('data-theme', 'light');
toggleSwitch.checked = false;
}
}
//listener for changing themes
toggleSwitch.addEventListener('change', switchTheme, false);
//pre-check the dark-theme checkbox if dark-theme is set
if (document.documentElement.getAttribute("data-theme") == "dark"){
toggleSwitch.checked = true;
}
finally, the HTML checkbox to toggle between themes:
<label id="theme-switch" class="theme-switch" for="checkbox_theme">
<input type="checkbox" id="checkbox_theme">
</label>
Through the use of CSS variables and JavaScript, we can automatically determine the users theme, apply it, and allow the user to over-ride it as well. [As of the current time of writing this (2019/06/10), only Firefox and Safari support the automatic theme detection]
Solution 2:
You can use my custom element <dark-mode-toggle> that initially adheres to the user's prefers-color-scheme setting, but that also allows the user to (permanently or temporarily) override it. The toggle works both with separate CSS files or with classes that are toggled. The README has examples for both approaches.
Solution 3:
Not sure, why all answers are so complicated.
Use CSS variables, set a default value, and an opposite value in a media query, as usual. Also set the values in two classes. Implement a toggle that toggles these classes when clicked.
By default, automatic light/dark mode is used based on the system color scheme. Using the toggle switches to manual light/dark mode. It returns to automatic light/dark mode after refreshing the page (or removing the class from the html element).
// toggle to switch classes between .light and .dark
// if no class is present (initial state), then assume current state based on system color scheme
// if system color scheme is not supported, then assume current state is light
function toggleDarkMode() {
if (document.documentElement.classList.contains("light")) {
document.documentElement.classList.remove("light")
document.documentElement.classList.add("dark")
} else if (document.documentElement.classList.contains("dark")) {
document.documentElement.classList.remove("dark")
document.documentElement.classList.add("light")
} else {
if (window?.matchMedia('(prefers-color-scheme: dark)').matches) {
document.documentElement.classList.add("light")
} else {
document.documentElement.classList.add("dark")
}
}
}/* automatic/manual light mode */
:root, :root.light {
--some-value: black;
--some-other-value: white;
}
/* automatic dark mode */
/* ❗️ keep the rules in sync with the manual dark mode below! */
@media (prefers-color-scheme: dark) {
:root {
--some-value: white;
--some-other-value: black;
}
}
/* manual dark mode
/* ❗️ keep the rules in sync with the automatic dark mode above! */
:root.dark {
--some-value: white;
--some-other-value: black;
}
/* use the variables */
body {
color: var(--some-value);
background-color: var(--some-other-value);
}<button onClick="toggleDarkMode()">Toggle</button>
<h1>Hello world!</h1>