Step 2: Style it with CSS variables

Now add a <style> block. Start with CSS variables (custom properties) on :root for the colours: --bg, --fg, --accent and --card. Everything else reads them with var(--accent). That means you can re-theme the whole page by changing a few lines, which we use in step 5 for dark mode.

Also set box-sizing: border-box on everything, a readable line-height, a maximum width for the main column, and a coloured header.

Examplehtml

<style>
:root { --bg: #ffffff; --fg: #1f2330; --accent: #0b6b4a; --card: #f1f3f5; }
* { box-sizing: border-box; }
body { margin: 0; font-family: system-ui, sans-serif; line-height: 1.6; background: var(--bg); color: var(--fg); }
header { background: var(--accent); color: #fff; padding: 28px 20px; text-align: center; }
header h1 { margin: 0; font-size: 2rem; }
nav { margin-top: 12px; }
nav a { color: #fff; margin: 0 10px; font-weight: 600; }
main { max-width: 860px; margin: 0 auto; padding: 20px; }
h2 { border-bottom: 3px solid var(--accent); display: inline-block; padding-bottom: 2px; }
footer { text-align: center; padding: 20px; color: #5b6270; }
</style>
<header>
  <h1>Ada Lovelace</h1>
  <p>Front-end developer in London</p>
  <nav aria-label="Main">
    <a href="#about">About</a>
    <a href="#projects">Projects</a>
    <a href="#contact">Contact</a>
  </nav>
</header>
<main>
  <section id="about">
    <h2>About me</h2>
    <p>I build fast, friendly websites and I love teaching others how the web works.</p>
  </section>
  <section id="projects">
    <h2>Projects</h2>
    <article><h3>Weather app</h3><p>A small app that shows the forecast.</p></article>
    <article><h3>Recipe finder</h3><p>Search recipes by ingredient.</p></article>
    <article><h3>Quiz game</h3><p>Test your web knowledge.</p></article>
  </section>
  <section id="contact">
    <h2>Contact</h2>
    <p>Say hello: ada@example.com</p>
  </section>
</main>
<footer><small>&copy; 2026 Ada Lovelace</small></footer>

Open in editor »

The accent green #0b6b4a was chosen because white text on it has a contrast ratio above 4.5:1, which meets the WCAG accessibility guideline. Try changing --accent and watch the headings, the header and the underlines change together.

Quick check

What does var(--accent) do?

Reads the value of the --accent custom propertyCreates a new variableImports a stylesheet

Finish the quick check (and any code exercise) to complete this lesson, or mark it done yourself.

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