DEV Community

Cover image for Understanding CSS Class and ID Selectors

Posted on

Understanding CSS Class and ID Selectors

Cascading Style Sheets (CSS) play an important role in defining the appearance of web pages. Class and ID selectors are among the many tools in a CSS developer's essentials. In this article, we'll dive more into the importance of these selectors, exploring their differences and providing practical examples to illustrate their usage.

Class Selectors

Class selectors in CSS play a crucial role in styling elements that share a common class attribute. Denoted by a period (.), followed by the class name, class selectors enable developers to apply consistent styles to multiple elements across a webpage.

In the code snippet below, we have three lines with distinct class attributes: number1, number 3, and number5. By defining corresponding styles in the CSS, we can ensure uniformity in appearance across these elements. For instance, we might specify a shared background color and font family for elements with these classes.

Example 1 Styling Elements with a Common Class

<p class="number1">Number 1 - I'm a class!</p>
<p class="number3">Number 3 - I'm a class, but cooler!</p>
<p class="number5">Number 5 - I'm a class!</p>
Enter fullscreen mode Exit fullscreen mode

Class selectors offer flexibility in web development, allowing for efficient styling of groups of elements without the need for repetitive inline styles or individual element targeting. This promotes cleaner, more maintainable code and facilitates cohesive design across a website. By mastering class selectors effectively, developers can streamline the styling process and achieve a consistent visual identity for their web projects.

ID Selectors

ID selectors in CSS are essential for targeting and styling individual elements uniquely within a web page. Identified by a hash (#) followed by the ID name, ID selectors enable developers to apply specialized styles to specific elements.

In the code snippet below, two <div> elements are present, each with a distinct ID attribute: number2 and number4. These IDs serve as unique identifiers for the respective elements Through employing ID selectors in CSS, developers can tailor styles specifically to these elements. This ensures precise control over their appearance and behavior.

Example 2 Styling Individual Elements with IDs

<div id="number2">Number 2 - I'm one ID.</div>
<div id="number4">Number 4 - I'm another ID.</div>
Enter fullscreen mode Exit fullscreen mode

Unlike class selectors, which can be applied to multiple elements sharing a common class attribute, ID selectors are intended for singular use. This specificity makes ID selectors ideal for styling elements with unique characteristics or functionalities.

By knowing and mastering ID selectors effectively, developers can enhance the visual presentation and usability of each element within their web pages. This achieves targeted styling and reinforces the overall design coherence.

Differences Between Class and ID Selectors:

It's important to understand the distinctions between class and ID selectors:

Classes are reusable and can be applied to multiple elements, whereas IDs should be unique within a document.
Specificity: ID selectors have higher specificity compared to class selectors. This means that styles applied through an ID selector will override styles applied through a class selector.
JavaScript Access: IDs are commonly used for JavaScript manipulation because they provide a unique identifier for elements.

Combining Selectors

Combining selectors in CSS empowers developers to target specific elements with precision, enhancing the flexibility and granularity of styling options. By combining different types of selectors, such as class and ID selectors, developers can tailor styles to meet precise design requirements.

In the example below, various elements are nested within a container <div> with the ID "container". By utilizing a combination of class and ID selectors, developers can apply styles to specific elements within this container while maintaining clarity and specificity.

Example 3 Combining Class and ID Selectors

<div id="container">
    <p class="number1">Number 1 - I'm a class!</p>
    <div id="number2">Number 2 - I'm one ID.</div>
    <p class="number3">Number 3 - I'm a class, but cooler!</p>
    <div id="number4">Number 4 - I'm another ID.</div>
    <p class="number5">Number 5 - I'm a class!</p>
Enter fullscreen mode Exit fullscreen mode

For instance, to style the paragraph with the class "number1", developers can use the selector "#container .number1". This selector targets elements with the class "number1" that are descendants of the element with the ID "container". Similarly, to style the <div> with the ID "number2", developers can use the selector "#container #number2", which directly targets the element with the ID "number2" within the container.

By knowing combined selectors strategically, developers can achieve precise and efficient styling, ensuring consistency and coherence across their web designs. This approach promotes modular and maintainable CSS code, facilitating easier management and scalability in larger projects.

Styling Overrides

In CSS, the concept of specificity dictates which styles take precedence when multiple rules target the same element. Specificity is determined by the combination of selectors used to target an element, with higher specificity granting precedence over lower specificity.

In the example below, two selectors target different elements within the HTML document. The .number3 selector targets elements with the class "number3", while the #number2 selector targets an element with the ID "number2".

Example 4 Specificity in Action

.number3 {
    font-size: 24px;
#number2 {
    color: RGB(0, 0, 255);
    font-size: 36px;
Enter fullscreen mode Exit fullscreen mode

Despite both selectors applying styles to different elements, they have different levels of specificity. IDs have a higher specificity than classes. Therefore, the style defined by the #number2 selector, specifying the font size as 36 pixels, will override the font size defined by the .number3 selector, which sets the font size to 24 pixels.

Understanding specificity is crucial for managing and debugging styles in CSS. By grasping how specificity influences style precedence, developers can write more effective and predictable CSS rules. Additionally, they can utilize techniques such as using more specific selectors or employing! important declarations when necessary to ensure desired styling outcomes and avoid unexpected override

when you run the style code, we see how different selectors work together to make things look nice on the webpage. Class selectors can style lots of things that are similar, while ID selectors focus on one thing at a time. When selectors team up, they create a special effect, making styles flow smoothly from one element to another. In this project, selectors work together like a team, making sure everything looks just right.

so  for you to get the  desired output using the code above, the following are steps you should use to  get the output using the VS Code follows

  1. Open VS Code First, open Visual Studio Code on your computer. You can find it in your applications folder or search for it in your system.

  2. Create Files: Within VS Code, create two new files. One should be named index.html and the other styles.css. You can do this by right-clicking in the explorer pane on the left side of VS Code, selecting "New File", and then typing in the file names.

  3. Write HTML: In the index.html file, write your HTML code. This likely includes the structure of your webpage, such as <html>, <head>, <title>, and <body>, as well as any content you want to display.

  4. Write CSS: In the styles.css file, write your CSS code. This will include styling instructions for your HTML elements, such as colors, fonts, and layout.

  5. Link CSS to HTML: In the index.html file, link the styles.css file to your HTML document. This is typically done within the <head> section of your HTML document using a <link>tag with the rel attribute set to "stylesheet" and the href attribute pointing to your styles.css file.


Copy code
<link rel="stylesheet" href="styles.css">
Enter fullscreen mode Exit fullscreen mode
  1. Run the Code Now that you have both HTML and CSS files set up, you can run the code snippet you have in your question. This might involve executing some JavaScript code or simply refreshing your browser if your code is purely HTML and CSS.

View Output After running the code, you should see the desired output in your web browser. This output will reflect the changes and styling applied through the HTML and CSS files you've created and linked as follows:

Image description


In conclusion, class and ID selectors stand as important tools in CSS for styling web pages. Their distinct characteristics and functionalities give developers the flexibility and control to create visually appealing and well-structured websites. While class selectors offer creativity for styling multiple elements with shared attributes, ID selectors provide a means to target individual elements uniquely.

Understanding the differences between these selectors and knowing when to utilize each is paramount for effective web development. By mastering the use of class and ID selectors, developers can streamline their CSS workflow, ensuring efficient styling and enhancing the overall user experience of their websites.

Top comments (0)