javascript - CSS module declaration doesn't work if I reference it on a specific body class

I am new to React and Gatsby.js. I am building a blog with Gatsby and my blog has a toggle to switch between light and dark modes. I am achieving this by toggling a class on the <body> tag with JavaScript. Essentially, if it is light mode, the tag will be <body> and if it is dark mode, the tag will be <body class="darkMode">.

I have managed to get this to work just fine by using vanilla JavaScript to set and remove the .darkMode class on the <body> tag. However, I am having some trouble styling elements based on body.darkMode in my CSS modules.

In my index.module.css file, I have the following classes:

.section {
  color: #141414;
}

body.darkMode .section {
  color: #ebebeb;
}

In my index.js ponent, I have imported the CSS module and applied the style like this:

<section className={indexStyles.section}></section>

While the color property in the .section class does work, I notice that the body.darkMode .section declaration does not work when I add the .darkMode CSS class to the <body> tag. Why is this? Help appreciated. Thanks.

In my index.module.css file, I have the following classes:

.section {
  color: #141414;
}

body.darkMode .section {
  color: #ebebeb;
}

In my index.js ponent, I have imported the CSS module and applied the style like this:

<section className={indexStyles.section}></section>

Share Improve this question asked May 19, 2019 at 19:10 JackH 4,7454 gold badges38 silver badges64 bronze badges

Can you show what styles are applied to the section when in dark mode from your dev tools? – Zlatko Commented May 19, 2019 at 19:24
Turns out that the body.darkMode .section line is also getting piled into a long class name like darkMode: "index-module--darkMode--3BMQh". Is there any way to prevent Gatsby from converting specific CSS declarations into its own random class names? – JackH Commented May 20, 2019 at 12:20
1 @Zlatko I managed to resolve this. See my answer in this thread. Thanks! – JackH Commented May 20, 2019 at 13:05

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2 Answers 2

Sorted by: Reset to default 7

I figured out the solution. It turns out, Gatsby was piling the body.darkMode .section into some arbitrary classnames. In reality, I wanted it to ignore body.darkMode but reference the local generated class name for .section.

I found the answer here - https://github./webpack-contrib/css-loader#scope. I was able to solve my specific issue by converting the original CSS to:

.section {
  color: #141414;
}

body:global(.darkMode) :local(.section) {
  color: #ebebeb;
}

As you can see, the :global and :local selectors allow you to target your HTML correctly.

if u want switch between Dark and Light Mode see this code

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

        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)
        }

@import url("https://fonts.googleapis./css?family=Poppins:300,400,900&display=swap");
html {
  width: 100%;
  height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background: var(--lightBg);
  --lightBtn: #FE016C;
  --lightBg: #fff;
  --lightColor: #232323;
}

html[data-theme='dark'] {
  background: var(--lightBg);
  --lightBtn: #FFBD07;
  --lightBg: #232323;
  --lightColor: #fff;
}

h1 {
  font-family: 'Poppins', sans-serif;
  font-weight: 300;
  color: var(--lightColor);
}

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

label {
  cursor: pointer;
  text-indent: -9999px;
  width: 55px;
  height: 30px;
  background: var(--lightBtn);
  margin: 0 auto;
  display: flex;
  justify-content: center;
  align-items: center;
  -webkit-border-radius: 100px;
  -moz-border-radius: 100px;
  border-radius: 100px;
  position: relative;
}

label:after {
  content: '';
  background: #fff;
  width: 20px;
  height: 20px;
  -webkit-border-radius: 50%;
  -moz-border-radius: 50%;
  border-radius: 50%;
  position: absolute;
  top: 5px;
  left: 4px;
  -webkit-transition: ease-in-out 200ms;
  -moz-transition: ease-in-out 200ms;
  -ms-transition: ease-in-out 200ms;
  -o-transition: ease-in-out 200ms;
  transition: ease-in-out 200ms;
}

input:checked + label {
  background: #FFBD07;
}

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

html.transition,
html.transition *,
html.transition *:before,
html.transition *:after {
  -webkit-transition: ease-in-out 200ms !important;
  -moz-transition: ease-in-out 200ms !important;
  -ms-transition: ease-in-out 200ms !important;
  -o-transition: ease-in-out 200ms !important;
  transition: ease-in-out 200ms !important;
  transition-delay: 0 !important;
}

 <div class="container">
        <h1>Light / Dark Mode</h1>

        <input class="container_toggle" type="checkbox" id="switch" name="mode">
        <label for="switch">Toggle</label>
    </div>

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javascript - CSS module declaration doesn't work if I reference it on a specific body class - Stack Overflow

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