Learn how to target an element with the id header using the CSS id selector.

Ever mess with the CSS that styles a page and thought, “How do I reach just this one spot?” If you’ve ever built a page with a distinct header, you’ve probably run into the id selector. It’s the clean, precise way to say, “Hey, browser, this is the one element I want you to style.”

Meet the id selector: #header

Here’s the thing to remember: in CSS, an id selector starts with a hash symbol (#) followed by the exact id value. So, to target an element that has id="header," you write #header in your CSS. Easy, right? It’s the shorthand you pull out when you want to affect a single, unique element—something that should be one-of-a-kind on the page.

If you’re comparing it to other selectors, the contrast is crisp:

• Class selectors use a period before the name, like .header. That targets every element with that class, not just one single element.

• Element (tag) selectors target a type of element, like header or div, regardless of its id or class. If you wrote header, it would apply to every header element on the page.

• The universal selector * grabs every element, which is handy for resets but not for fine-tuning a single piece of the layout.

Let me explain with a quick real-world example

Suppose you’re building a simple landing page. Your header section needs a bold background color and extra padding. You’ll likely mark the header element with an id so that only the header gets this styling:

• HTML:

  Site Header

• CSS: #header { background: #333; color: white; padding: 16px; }

This pairing ensures only that header takes on the dark background and extra breathing room. If you used a class, you might apply the same look to multiple sections, which isn’t what you want when you’re aiming for a distinct, recognizable top bar.

Why use an id at all?

Ids are unique by design. In HTML, you should assign a single id to one element. That uniqueness is part of the CSS specificity game, which can feel a little nerdy but is incredibly practical when you’re trying to keep styles predictable as your project grows. When you know there’s only one header in your layout with id="header," you won’t accidentally style another element in a way that surprises you later.

Ids also shine in JavaScript. If you ever need to grab that exact element to toggle a class or read its value, an id is a clean, fast hook. It’s not all about visuals—interactivity loves precise targets.

A couple of practical notes

• Make sure the id is unique within the document. If two elements share id="header," your CSS will still apply to both, but that violates the idea of an id as a unique handle. Browsers will still apply the styles, but your code becomes confusing to maintain.

• If you find yourself reusing the same visual style in more than one place, a class is a better fit. Classes are intended for that kind of repetition, while ids mark the one-off personalities in your page structure.

• If you’re tuning the header’s look across breakpoints (responsive design), you’ll often combine the id selector with media queries. For example, you might keep #header styling steady on desktop but tweak padding on smaller screens:

@media (max-width: 600px) {

#header { padding: 12px; }

}

A tiny history detour that still helps

In the early days of CSS, people loved to use ids for everything because they felt fast and precise. Over time, developers learned to mix in classes and structural selectors to keep styles scalable. The key idea is balance: use an id when you truly need a unique target, and lean on classes for patterns you see again and again. That blend keeps a project tidy and easier to maintain when new features roll in.

Common misunderstandings worth clearing up

• Some folks think an id selector must live in its own file. Not at all. You can place #header in the same stylesheet as other rules. It’s just another selector with its own set of styles.

• Don’t rely on an id to drive layout decisions alone. Id selectors don’t inherently become more important than class selectors in the cascade. Specificity still matters, and a higher specificity can override what you expect if you’re not careful.

• It’s tempting to name an id after the tag, like id="header" for a

  element. That’s fine, but avoid making it too generic if you’ll be working on a large project. A clear, descriptive id helps you understand the intent at a glance.

A few quick tips to sharpen your CSS sense

• Practice with dev tools: open Chrome DevTools or Firefox Developer Tools, select the element, and peek at the computed styles. You’ll see exactly which rules apply—and in what order.

• Keep an eye on specificity. If you find your #header styles aren’t applying the way you expect, check for inline styles or more specific selectors that might be winning the fight.

• Use semantic structure where possible. If your page has a real header element, you can still give it an id for targeted styling without breaking the meaning of your HTML. For accessibility and clarity, combine semantic tags with precise selectors.

A friendly nudge toward broader CSS wisdom

You’ll notice that CSS isn’t just about “what looks good,” but also about “how it behaves in the browser.” The id selector is a great gateway into that mindset. As you experiment, you’ll start appreciating the choreography between markup, styles, and the way devices render pages. Revature topics often circle back to this balance— understanding the foundations makes it easier to grasp more advanced topics later on, like CSS variables, grid layouts, and responsive design patterns.

If you’re curious about where this all fits in the bigger picture, here’s a quick mental map:

• HTML gives you the structure and the hooks (like id="header").

• CSS uses selectors to dress those hooks with visuals.

• The cascade, specificity, and inheritance decide which styles actually win.

• JavaScript can enhance interactivity by toggling or reading an element’s state.

A final example to tie it all together

Let’s say you’ve got a header that should look bold on desktop but a bit softer on mobile. You might do something like:

• HTML:

  My Awesome Site

• CSS:

#header { background: #222; color: #fff; padding: 20px; font-family: Arial, sans-serif; }

@media (max-width: 600px) {

#header { padding: 12px; font-size: 16px; }

}

That’s the practical edge of the id selector in action: a single, reliable target that adapts gracefully to different screen sizes without sprawling CSS.

For the curious mind, a small mental experiment

If you opened a blank page and started with a single element:

, you could paint that one element with as much personality as you want. The id selector gives you a direct, unambiguous line to that personality. It’s like tapping a single control on a dashboard and seeing the whole section respond, instantly.

Wrapping it up

So, when you see an element that should stand out as unique—a top bar, a hero’s headline, a special callout—the #header selector is your go-to move. It’s clean, it’s precise, and it plays nicely with the rest of your CSS toolkit. And because this is the kind of knowledge that compounds—as you learn to pair it with classes, structural selectors, and media queries—you set yourself up for smoother, more scalable styling down the road.

If you’re exploring more CSS ideas, you’ll find that the same mindset applies across the board: understand the hook, pick the right selector, and test how it behaves in real pages. It’s a small skill, but it compounds into a very usable fluency—one that makes front-end work feel a lot less chaotic and a lot more satisfying.