What is the Difference Between ID and Class in CSS?

When styling elements in CSS, two of the most commonly used selectors are ID (#) and Class (.). Both allow you to apply styles to elements, but they have distinct differences in terms of usage, specificity, and best practices.

In this blog, we will explore the difference between ID and Class in CSS, how to use them, and when to choose one over the other.

1. What is an ID in CSS?

An ID is a unique identifier for a single element on a webpage. It is defined using the id attribute in HTML and targeted in CSS using a # symbol.

Example of ID Usage

HTML:

<p id="unique-text">This is a paragraph with a unique ID.</p>

CSS:

#unique-text {
    color: blue;
    font-size: 20px;
    font-weight: bold;
}

✅ Key Points About ID:

• An ID must be unique within an HTML document.
• It has higher specificity than a class.
• It should be used for elements that appear only once on a page (e.g., a logo, main header, or footer).

---

2. What is a Class in CSS?

A Class is a reusable selector that applies styles to multiple elements. It is defined using the class attribute in HTML and targeted in CSS using a . (dot) symbol.

Example of Class Usage

HTML:

<p class="highlight">This is a highlighted paragraph.</p>
<p class="highlight">This is another highlighted paragraph.</p>

CSS:

.highlight {
    background-color: yellow;
    padding: 10px;
    font-size: 18px;
}

✅ Key Points About Class:

• A class can be assigned to multiple elements.
• It is more flexible than an ID and promotes reusability.
• It has lower specificity than an ID.

---

3. Key Differences Between ID and Class

Feature	ID (#id)	Class (.class)
Uniqueness	Must be unique in a document	Can be used on multiple elements
Symbol	#id	.class
Specificity	Higher specificity	Lower specificity
Reusability	Used for single elements	Used for multiple elements
Best for	Unique elements like headers, navigation bars, or sections	Groups of elements like buttons, text blocks, or styling multiple elements similarly

---

4. When to Use ID vs. Class?

✅ Use an ID (#) when:

• The element is unique and appears only once on the page.
• You need to apply JavaScript interactions (e.g., document.getElementById("id")).

✅ Use a Class (.) when:

• You need to style multiple elements with the same properties.
• You want a reusable and scalable CSS structure.

---

5. Can You Use ID and Class Together?

Yes! An element can have both an ID and a class.

Example:

<p id="main-text" class="highlight">This paragraph has both an ID and a class.</p>

CSS:

#main-text {
    color: red;
}

.highlight {
    background-color: yellow;
}

This paragraph will have both red text color (from the ID) and a yellow background (from the class).

---

6. Which One Should You Use?

In general, classes are preferred over IDs in CSS for styling because they offer better flexibility and reusability. IDs should be reserved for unique elements or JavaScript interactions.

🔹 Best Practice: Use classes for styling and IDs for JavaScript or unique elements.

---

Conclusion

• ID (#) is unique and should be used for single elements.
• Class (.) is reusable and should be used for multiple elements.
• Classes are more flexible and better for styling, while IDs are better for JavaScript interactions.