Class-based dark mode strategy in Tailwind - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable dark mode using a class in Tailwind CSS.

Tailwind

<html class="[1]">
  <body>
    <h1 class="text-black dark:text-white">Hello, world!</h1>
  </body>
</html>

Drag options to blanks, or click blank then click option'

Adark-mode

Bdark

Cnight

Dtheme-dark

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dark-mode' or other class names instead of 'dark'.

Placing the class on the instead of .

The dark class on the html element activates Tailwind's dark mode styles.

2fill in blank

medium

Complete the Tailwind config to enable class-based dark mode.

Tailwind

module.exports = {
  darkMode: '[1]',
  theme: {
    extend: {},
  },
  plugins: [],
}

Drag options to blanks, or click blank then click option'

A"class"

B"auto"

C"manual"

D"media"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'media' which relies on system settings.

Using unsupported values like 'auto' or 'manual'.

Setting darkMode to "class" tells Tailwind to use a class to toggle dark mode.

3fill in blank

hard

Fix the error in the JavaScript code that toggles dark mode by adding or removing the correct class on the <html> element.

Tailwind

const html = document.documentElement;
function toggleDarkMode() {
  if (html.classList.contains('[1]')) {
    html.classList.remove('dark');
  } else {
    html.classList.add('dark');
  }
}

Drag options to blanks, or click blank then click option'

Adark

Bdark-mode

Cnight

Dtheme-dark

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for a different class than the one added or removed.

Using 'dark-mode' or other incorrect class names.

The class to check and toggle is dark, matching Tailwind's dark mode class.

4fill in blank

hard

Fill both blanks to create a button that toggles dark mode on click.

Tailwind

<button onclick="document.documentElement.classList.[1]('[2]')">
  Toggle Dark Mode
</button>

Drag options to blanks, or click blank then click option'

Atoggle

Badd

Cdark

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' or 'remove' instead of 'toggle'.

Using the wrong class name.

The toggle method adds the class if missing or removes it if present. The class to toggle is dark.

5fill in blank

hard

Fill all three blanks to create a dark mode toggle that saves the preference in localStorage and applies it on page load.

Tailwind

<script>
  const html = document.documentElement;
  const toggle = () => {
    html.classList.[1]('dark');
    if (html.classList.contains('dark')) {
      localStorage.setItem('[2]', '[3]');
    } else {
      localStorage.removeItem('[2]');
    }
  };
  if (localStorage.getItem('[2]') === '[3]') {
    html.classList.add('dark');
  }
</script>

Drag options to blanks, or click blank then click option'

Atoggle

Bdark-mode

Cenabled

Ddark

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' or 'remove' instead of 'toggle'.

Using inconsistent localStorage keys or values.

Not applying the class on page load.

The toggle method switches the 'dark' class. The localStorage key is 'dark-mode' and the value saved is 'enabled' to remember the preference.

Practice

1. What does the dark: prefix in Tailwind CSS do when using class-based dark mode?

easy

A. Applies styles only when a parent element has the dark class.

B. Automatically detects system dark mode and applies styles.

C. Adds a dark background color to all elements.

D. Disables all light mode styles on the page.

Solution

1. Step 1: Understand the dark: prefix role

   The dark: prefix in Tailwind applies styles only when the dark class is present on a parent element.

2. Step 2: Compare with other options

   It does not auto-detect system settings or disable light styles; it depends on the dark class presence.

3. Final Answer:

   Applies styles only when a parent element has the dark class. -> Option A

4. Quick Check:

   dark: prefix = styles with dark class [OK]

Hint: Remember: dark: works only if dark class exists [OK]

Common Mistakes:

• Thinking dark: auto-detects system dark mode
• Assuming it changes styles without the dark class
• Confusing dark: with global dark mode toggle

2. Which of the following is the correct way to enable dark mode using class strategy in Tailwind CSS?

easy

A. "darkMode: 'media'" in tailwind.config.js

B. "darkMode: 'class'" in tailwind.config.js

C. Adding dark attribute to body tag

D. Using dark-mode class instead of dark

Solution

1. Step 1: Check Tailwind config for dark mode strategy

   To use class-based dark mode, you must set darkMode: 'class' in tailwind.config.js.

2. Step 2: Eliminate other options

   darkMode: 'media' uses system preference, not class. The dark class must be added manually; no dark attribute exists. The class name must be exactly dark.

3. Final Answer:

   "darkMode: 'class'" in tailwind.config.js -> Option B

4. Quick Check:

   Config setting for class strategy = 'class' [OK]

Hint: Set darkMode to 'class' in config for class-based dark mode [OK]

Common Mistakes:

• Using 'media' instead of 'class' in config
• Adding wrong attribute instead of class
• Using incorrect class name like 'dark-mode'

3. Given this HTML snippet:

<html class="dark">
  <body>
    <div class="bg-white dark:bg-gray-800 text-black dark:text-white p-4">Hello</div>
  </body>
</html>

What background and text colors will the <div> have when rendered?

medium

A. Background white, text black

B. Background gray-800, text black

C. Background gray-800, text white

D. Background white, text white

Solution

1. Step 1: Identify presence of dark class

   The <html> tag has the dark class, so all dark: styles apply.

2. Step 2: Apply styles based on class

   The div has bg-white and text-black normally, but with dark:bg-gray-800 and dark:text-white when dark class is present. So background is gray-800 and text is white.

3. Final Answer:

   Background gray-800, text white -> Option C

4. Quick Check:

   Dark class present = dark styles apply [OK]

Hint: If dark class exists, dark: styles override [OK]

Common Mistakes:

• Ignoring the dark class on html
• Mixing normal and dark styles incorrectly
• Assuming no style changes without JavaScript

4. You want to toggle dark mode by adding/removing the dark class on body. Which of these JavaScript snippets correctly toggles dark mode?

medium

A. document.body.setAttribute('dark', true)

B. document.body.toggleClass('dark')

C. document.body.className = 'dark'

D. document.body.classList.toggle('dark')

Solution

1. Step 1: Understand class toggling in JavaScript

   The correct method to toggle a class is classList.toggle('className').

2. Step 2: Check each option

   document.body.classList.toggle('dark') uses classList.toggle('dark'), which is correct. document.body.toggleClass('dark') uses a non-existent toggleClass method. document.body.className = 'dark' overwrites all classes, removing others. document.body.setAttribute('dark', true) sets an attribute, not a class.

3. Final Answer:

   document.body.classList.toggle('dark') -> Option D

4. Quick Check:

   Toggle class method = classList.toggle [OK]

Hint: Use classList.toggle('dark') to switch dark mode on/off [OK]

Common Mistakes:

• Using jQuery method toggleClass in plain JS
• Replacing className instead of toggling
• Setting attribute instead of class

5. You want to create a button that toggles dark mode by adding/removing the dark class on the html element. Which React code snippet correctly implements this using Tailwind's class-based dark mode?

hard

A. const toggleDark = () => { document.documentElement.classList.toggle('dark'); };

return Toggle Dark;

B. const toggleDark = () => { document.body.classList.add('dark'); };

return Toggle Dark;

C. const toggleDark = () => { document.documentElement.setAttribute('dark', 'true'); };

return Toggle Dark;

D. const toggleDark = () => { document.body.className = 'dark'; };

return Toggle Dark;

Solution

1. Step 1: Identify correct element and method for toggling

   Tailwind's class-based dark mode expects the dark class on the html element (document.documentElement). Toggling means adding or removing the class, so classList.toggle is best.

2. Step 2: Evaluate each option

   const toggleDark = () => { document.documentElement.classList.toggle('dark'); }; return Toggle Dark; toggles dark on html correctly. const toggleDark = () => { document.body.classList.add('dark'); }; return Toggle Dark; only adds dark to body (no toggle). const toggleDark = () => { document.documentElement.setAttribute('dark', 'true'); }; return Toggle Dark; sets an attribute instead of class. const toggleDark = () => { document.body.className = 'dark'; }; return Toggle Dark; overwrites all classes on body, removing others.

3. Final Answer:

   const toggleDark = () => { document.documentElement.classList.toggle('dark'); }; return <button onClick={toggleDark}>Toggle Dark</button>; -> Option A

4. Quick Check:

   Toggle dark class on html with classList.toggle [OK]

Hint: Toggle dark class on html using classList.toggle [OK]

Common Mistakes:

• Adding class without toggling
• Using wrong element like body
• Setting attribute instead of class
• Overwriting all classes instead of toggling