CSS stands for Cascading Style Sheets, and it’s a simple mechanism that tells your browser how to display web pages written up in HTML or another markup language. And just like HTML and JavaScript, CSS is one of the key technologies of the World Wide Web.

But in today’s increasingly competitive job market, prospective employers don’t just ask, what is CSS? Candidates for web developer positions and similar roles are expected to be proficient with this technology. Keep reading to find out everything you need to know about CSS.

Stylesheet Fundamentals

CSS is a stylesheet language that enables users to create outstanding-looking pages across all browsers. It can manipulate basic document text stylings such as size, color, links, and headings. CSS can also be used to turn a single column into multiple columns or add animations and other visuals.      

In other words, CSS is a styling language that makes life easier for developers by simplifying and speeding up their work while improving the overall experience for web page visitors. As such, CSS is an important tool for web specialists everywhere.

CSS Basics

While implementing layout, font, and colors onto an HTML document, CSS uses a straightforward syntax that is easy to learn. The CSS stylesheet language relies on a list of rules. Every rule is defined by at least one selector and a declaration block. In the CSS language, if you set the rule where the main heading has to be shown in a large blue text, you'll use the following code:

h1 {

color: red;

font-size: 5em;



This code begins with the selector (<h1>), which marks the HTML element we want to style. A CSS language selector can either identify a single element (ID selector) or group together multiple HTML elements, which is referred to as a CSS class selector. 

One of the significant benefits of using selectors is the option to combine them in several ways to get more flexibility while working on an HTML website. You can mix them in a spaced list to designate elements by ID, class, location, or element type. While describing the presentation of a document in HTML using the CSS language, it’s important to be mindful of the order of the selectors, as they can change the elements we want to style.

Declaration Block

Declarations are property and value pairs that are placed within curly braces. Every pair defines a property of one or more elements that we are choosing, along with a value that we want to give to the property. We also have a colon (:) that separates the property and value. If we have more than one declaration in a block, we'll use a semicolon (;) as a separator.

CSS is the best stylesheet language because you can include different values in properties. For instance, the color property can have various color values such as keywords (“red”), RGB scale value (rgb(255, 0, 0)), hexadecimal color value (#FF0000), and more. You can also include the font size with the property taking on several size units.

The Importance of CSS

Before the birth of CSS, HTML text files were contained in the HTML markup. Developers could include background styles, element alignments, borders, font colors, and size with HTML. However, they had to assign presentational properties to each element by repeating the same code within the document multiple times.

The main purpose of CSS is to reduce the risk of errors. Also, the messy HTML markup was reducing page load speeds due to the size of the HTML code. CSS separated the document and presentation, thus reducing loading times. The elementary CSS syntax sped up the process of code debugging. It reduced the constant code repetition for the same elements in the document by introducing selectors and declarations. All of this was made possible thanks to two factors.

CSS Modules

CSS uses modules to simplify and unify the development of this language. Thanks to the evolution of the CSS language, modules allow for easy referencing and quick searches in the MDN database. The official list of CSS specifications shows many modules in various stages of development and variation.

The language itself has three levels: CSS 1, CSS 2, and CSS 3. Each one introduces fundamental improvements and changes to the language. After the CSS 3 variation, the development is measured in modules that allow various CSS features to develop at different speeds.

CSS Specifications

So, what type of language is CSS? The exact details of this program are outlined in giant specifications documents that are compiled by experts and representatives of browser vendors. CSS features are developed and specified by the CSS Working Group, which operates within one of the standards organizations, W3C.

The integration of new features in CSS specifications enables the CSS file to be easily added to the document while maintaining a high level of browser compatibility. It means that an HTML/CSS page in Google Chrome will be nearly identical when displayed in Firefox Mozilla, Microsoft Edge, or Opera, with only minor changes.

The W3C group and the specifications document also monitor that new improvements are compatible with the older CSS variants. All new capabilities of CSS should not crash older HTML websites. That is why many decades-old websites still work.

Benefits of Using CSS

CSS is a highly useful tool for a number of reasons. We’ve outlined some of the key ones below:

  • Quicker Page Speeds - A CSS rule can be used for many selectors with a specific tag, reducing the code's size and improving site performance.
  • Improved Development Times - With one code string in CSS, you can implement a formatting style or rule across several HTML websites. 
  • Enhanced User Experience - CSS not only brings a better visual overhaul of the site, but it adds superior user-friendly formatting elements as well.
  • Straightforward Formatting Adjustments - Thanks to CSS, the introduction and manipulation of a format on specific pages are possible. When you change a CSS stylesheet, that change will be applied across all style sheet-related pages.
  • Device Compatibility - CSS can be made compatible with all browsers, and it can be used with smart TVs, desktop devices, mobile gaming apps, and more.

Disadvantages of Using CSS

There is no perfect computer language. While constant improvements eliminated many pre-existing limitations, there are several disadvantages of using CSS:

  • Selectors cannot move up - CSS isn't a programming language, and the inclusion of an element's parent or ancestor is not possible unless it's a part of the whole selector profile. Such selectors would bring browser performance and incremental rendering degradation.
  • Rules cannot be named - Client-sized scripts that refer to the rule despite the changes with the selector are not possible in CSS.
  • There are no adding rule styles into a different rule - You have to make a copy of a CSS style for every rule, which prolongs debugging and testing periods.
  • You have to change the markup to target specific text - In other words, you have to use place-holder elements to aim specific ranges of text in CSS language.
  • Managing pseudo-class dynamic behavior is not possible - Except for partial management of one dynamic CSS pseudo-class (:hover), a client cannot disable or limit the effects of pseudo-classes.


Separating presentation and content, CSS is an essential technology for describing documents written in markup languages such as HTML. Of course, knowing how to navigate this technology is an important skill in the IT sector. CSS is credited with introducing many cornerstone improvements used by the vast majority of web pages today.