CSS Selectors: Class and ID Explained

If you’re learning CSS, one of the first confusing topics is the difference between class and ID selectors.

Both are used to style elements but they are not the same.

In this guide, you’ll learn:

• The difference between class and ID in CSS
• When to use each one
• Real-world use cases
• Best practices developers follow

Let’s simplify it.

What Is a Class in CSS?

A class is a reusable selector used to style multiple elements.

Example

<p class="highlight">First paragraph</p>
<p class="highlight">Second paragraph</p>

.highlight {
color: blue;
}

Both paragraphs will turn blue.

Key Characteristics of Class

• Reusable
• Can be used on multiple elements
• An element can have multiple classes
• Written with a dot . in CSS

Example of multiple classes:

<button class="btn primary large">Click Me</button>

What Is an ID in CSS?

An ID is a unique selector used to style one specific element.

Example

<h1 id="main-title">Welcome</h1>

#main-title {
color: red;
}

Only that element will turn red.

Key Characteristics of ID

• Must be unique on the page
• Used only once
• Written with a hash # in CSS
• Higher specificity than class

Main Differences Between Class and ID

1. Reusability

Class → Can be reused multiple times
ID → Should be used only once

2. Specificity

ID has higher CSS specificity than class.

Example:

#box {
color: red;
}
.box {
color: blue;
}

If both apply to the same element, red wins because ID is stronger.

3. Multiple Usage

You can assign:

Multiple classes to one element ✅
Only one ID per element ✅
But the same ID should not appear multiple times ❌

When to Use Class

Use class when:

• Styling multiple elements the same way
• Creating reusable components
• Designing buttons, cards, layouts
• Applying utility styles

Example use cases:

<div class="card"></div>
<div class="card"></div>
<div class="card"></div>

Classes are ideal for scalable design.

When to Use ID

Use ID when:

• Targeting a single unique section
• Creating page anchors
• JavaScript DOM targeting (sometimes)
• Major layout sections

Example:

<section id="hero"></section>

IDs are good for unique structural parts.

Best Practice: Prefer Classes

In modern development, most developers prefer classes over IDs for styling.

Why?

• Better scalability
• More flexible
• Easier to maintain
• Works better with component-based design

Frameworks like Tailwind, Bootstrap, and modern UI libraries rely heavily on classes.

Common Mistakes

1. Using ID for styling everything ❌
2. Repeating the same ID multiple times ❌
3. Overusing high-specificity selectors ❌

Keeping specificity low makes CSS easier to manage.

Quick Comparison Table

Class:

• Syntax: .classname
• Reusable: Yes
• Specificity: Medium
• Best for: Reusable styles

ID:

• Syntax: #idname
• Reusable: No
• Specificity: High
• Best for: Unique elements

Conclusion

The difference between class and ID in CSS comes down to reusability and specificity.

Use classes for styling multiple elements and building scalable designs.
Use IDs for unique sections or specific purposes.

At Developer Hint, we recommend keeping your CSS flexible and maintainable and that usually means relying more on classes than IDs.

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