What Is CSS?

CSS stands for cascading style sheets and is an element of front-end development responsible for determining the overall styling and layout of a web page.

Written by Anthony Corbo
Published on Dec. 29, 2022
What Is CSS?
Image: Shutterstock / Built In
Brand Studio Logo
Omar Rabbolini | Jan 05, 2023

CSS (cascading style sheets) works in conjunction with HTML and is directly responsible for dictating color, background, text color, font, positioning and additional features to the web browser. CSS is a key component of web development.

Is CSS a Programming Language?

CSS is not recognized as a programming language by developers because it is only responsible for determining front-end styling. CSS contains no instructions on how the site should function or make decisions, unlike other front-end and back-end languages. Instead, CSS is a stylesheet language often added to a website’s directory by developers as a separate file and works with JavaScript and HTML to determine the site’s front-end appearance. CSS is directly responsible for dictating how background color, font styling, layouts, borders, shadowing and more will appear on the page, making it an essential tool for any website project.

More on Built InCan Low-Code Tools End the Developer Shortage?


HTML vs. CSS: What’s the Difference?

Although HTML and CSS are closely related, CSS determines style whereas HTML determines content and structure.

CSS and HTML work together with different areas of focus to create the webpage a user sees. These differing foci result because CSS is a stylesheet language, whereas HTML is a markup language. So, HTML structures web pages with elements like headers, paragraphs and lists while CSS contains the style information for those structures. While neither HTML or CSS is more complex than the other in terms of syntax, a major difference is that HTML can contain CSS within its code and files, but CSS cannot contain HTML. Both HTML and CSS are mutually containing, however, meaning CSS and HTML share tag names with each other.

CSS in 100 Seconds. | Video: Fireship


What Does Responsive Mean in CSS?

Responsive web design means the CSS uses flexible layouts, images and other techniques to style the page automatically for various screen sizes.

Modern web pages are viewable on multiple devices with variously sized screens and layouts. Additionally, most common laptop and desktop computers allow windows that software and browsers launch to be reshaped into various sizes. This resizing posed a challenge for CSS developers and caused errors in layout and font placement until the development of responsive web design.

Instead of using fixed-width parameters, in responsive web design, CSS uses X- and Y-coordinates on a grid along with mathematical percentages to determine where assets should be placed based on the current size of the window or another reference point, such as a printer. CSS2, an evolution of CSS, incorporated media queries to allow developers to specify triggers for certain styles to take effect. For example, it can present a printer-friendly version of the page when requested. CSS3 took this a step further by introducing query capabilities to respond to the dimensions of a viewport or a device, the portrait or landscape orientation of the device and the screen resolution.

Find out who's hiring.
See all Developer + Engineer jobs at top tech companies & startups
View 10000+ Jobs
Hiring Now
Mondelēz International
Big Data • Food • Hardware • Machine Learning • Retail • Automation • Manufacturing