What Is CSS? Cascading Style Sheets Explained And History
CSS stands for Cascading Style Sheets. It is a style sheet language which is used to describe the look and formatting of a document written in markup language. It provides an additional feature to HTML. It is generally used with HTML to change the style of web pages and user interfaces. It can also be used with any kind of XML documents including plain XML, SVG and XUL.
CSS is used along with HTML and JavaScript in most websites to create user interfaces for web applications and user interfaces for many mobile applications.
What does CSS do
- You can add new looks to your old HTML documents.
- You can completely change the look of your website with only a few changes in CSS code.
Advantages of CSS
- CSS saves time − You can write CSS once and then reuse same sheet in multiple HTML pages. You can define a style for each HTML element and apply it to as many Web pages as you want.
- Pages load faster − If you are using CSS, you do not need to write HTML tag attributes every time. Just write one CSS rule of a tag and apply it to all the occurrences of that tag. So less code means faster download times.
- Easy maintenance − To make a global change, simply change the style, and all elements in all the web pages will be updated automatically.
- Superior styles to HTML − CSS has a much wider array of attributes than HTML, so you can give a far better look to your HTML page in comparison to HTML attributes.
- Multiple Device Compatibility − Style sheets allow content to be optimized for more than one type of device. By using the same HTML document, different versions of a website can be presented for handheld devices such as PDAs and cell phones or for printing.
- Global web standards − Now HTML attributes are being deprecated and it is being recommended to use CSS. So its a good idea to start using CSS in all the HTML pages to make them compatible to future browsers.
How Does CSS Work?
CSS brings style to your web pages by interacting with HTML elements. Elements are the individual HTML components of a web page—for instance a paragraph—which in HTML might look like this:
<p>This is my paragraph!</p>
If you wanted to make this paragraph appear pink and bold to people viewing your web page through a web browser, you’d use CSS code that looks like this:
p { color:pink; font-weight:bold; }In this case, “p” (the paragraph) is called the “selector”—it’s the part of CSS code specifying which HTML element the CSS styling will effect. In CSS, the selector is written to the left of the first curly bracket. The information between curly brackets is called a declaration, and it contains properties and values that are applied to the selector. Properties are things like font size, color, and margins, while values are the settings for those properties. In the example above, “color” and “font-weight” are both properties, and “pink” and “bold” are values. The full bracketed set of
{ color:pink; font-weight:bold; }is the declaration, and again, “p” (meaning the HTML paragraph) is the selector. These same basic principles can be applied to change font sizes, background colors, margin indentations, and more. For instance. . .
body { background-color:lightblue; }. . .would make your page’s background light blue, or. . .
p { font-size:20px; color:red; }. . .will create a 20 point font paragraph with red letters.
External, Internal and Inline CSS?
You might be wondering how this CSS code is actually applied to HTML content, though. Much like HTML, CSS is written in simple, plain text through a text editor or word processor on your computer, and there are three main ways to add that CSS code to your HTML pages. CSS code (or Style Sheets) can be external, internal, or inline. External style sheets are saved as .css files and can be used to determine the appearance of an entire website through one file (rather than adding individual instances of CSS code to every HTML element you want to adjust). In order to use an external style sheet, your .html files need to include a header section that links to the external style sheet and looks something like this:
<head>
<link rel=”stylesheet” type=”text/css” href=mysitestyle.css”>
</head>
This will link the .html file to your external style sheet (in this case, mysitestyle.css), and all of the CSS instructions in that file will then apply to your linked .html pages.
Internal style sheets are CSS instructions written directly into the header of a specific .html page. (This is especially useful if you have a single page on a site that has a unique look.) An internal style sheet looks something like this. . .
<head>
<style>
body { background-color:thistle; }
P { font-size:20px; color:mediumblue; }
</style>
</head>
. . . a thistle background color and paragraphs with 20 point, medium blue font will now be applied to this single .html page.
Finally, inline styles are snippets of CSS written directly into HTML code, and applicable only to a single coding instance. For example:
<h1 style=”font-size:40px;color:violet;”>Check out this headline!</h1>
CSS syntax
CSS is a rule-based language — you define rules specifying groups of styles that should be applied to particular elements or groups of elements on your web page. For example "I want the main heading on my page to be shown as large red text."
The following code shows a very simple CSS rule that would achieve the styling described above:
h1 {
color: red;
font-size: 5em;
}The rule opens with a selector . This selects the HTML element that we are going to style. In this case we are styling level one headings (<h1>).
We then have a set of curly braces { }. Inside those will be one or more declarations, which take the form of property and value pairs. Each pair specifies a property of the element(s) we are selecting, then a value that we'd like to give the property.
Before the colon, we have the property, and after the colon, the value. CSS properties have different allowable values, depending on which property is being specified. In our example, we have the color property, which can take various color values. We also have the font-size property. This property can take various size units as a value.
A CSS stylesheet will contain many such rules, written one after the other.
h1 {
color: red;
font-size: 5em;
}
p {
color: black;
}
You will find that you quickly learn some values, whereas others you will need to look up. The individual property pages on MDN give you a quick way to look up properties and their values when you forget, or want to know what else you can use as a value.
Who Creates and Maintains CSS?
CSS is created and maintained through a group of people within the W3C called the CSS Working Group. The CSS Working Group creates documents called specifications. When a specification has been discussed and officially ratified by the W3C members, it becomes a recommendation.
These ratified specifications are called recommendations because the W3C has no control over the actual implementation of the language. Independent companies and organizations create that software.
NOTE − The World Wide Web Consortium, or W3C is a group that makes recommendations about how the Internet works and how it should evolve.
CSS Versions
Cascading Style Sheets level 1 (CSS1) came out of W3C as a recommendation in December 1996. This version describes the CSS language as well as a simple visual formatting model for all the HTML tags.
CSS2 became a W3C recommendation in May 1998 and builds on CSS1. This version adds support for media-specific style sheets e.g. printers and aural devices, downloadable fonts, element positioning and tables.
Note: All information is collected online.
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