CSS Variables

Reusable custom properties.

✍️ 3 exercises + code challenge in this lesson

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CSS variables (custom properties) store values you want to reuse, such as brand colours.

Declare them with two dashes: --primary: #2563EB;
Read them with var(): color: var(--primary);
Declaring them on :root makes them available everywhere.
A fallback can be given: var(--accent, orange).

Variables can be changed in media queries or with JavaScript, which makes themes like dark mode easy.

Key Takeaways: CSS Variables

Mastering CSS Variables helps you write clean and reliable CSS code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

CSS Variables Code Example

CSS

<style>
  :root { --primary: #2563EB; --accent: #14B8A6; --radius: 10px; }
  .dark { --primary: #38BDF8; background: #071A2F; color: white; }

  .panel  { padding: 16px; border-radius: var(--radius); margin-bottom: 10px; border: 2px solid var(--primary); }
  .panel h3 { color: var(--primary); margin: 0 0 6px; }
  .btn    { background: var(--accent); color: white; border: 0; padding: 8px 14px; border-radius: var(--radius); }
</style>

<div class="panel"><h3>Light theme</h3><button class="btn">Button</button></div>
<div class="panel dark"><h3>Dark theme</h3><button class="btn">Button</button></div>

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CSS Variables Practice Exercises

Check what you learned in “CSS Variables”.

/ 3 solved

Fill in the blank

Read the custom property --brand.

button {
  background: (--brand);
}

✓ Correct! Not quite. Try again.

Multiple choice

Where should global CSS variables usually be declared?

:root body only html only via JavaScript In each element

✓ Correct! Not quite. Try again.

Code challenge

Declare --main-color: #14b8a6 on :root and use it as the colour of h1.

Write the code in the live editor. Your answer is checked automatically.

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CSS Variables

💡 Key Takeaways: CSS Variables

CSS Variables Code Example

CSS Variables Practice Exercises

Key Takeaways: CSS Variables