CSS
CSS stands for Cascading Style Sheets. CSS is a style sheet language used for describing the presentation of a document written in HTML. It was designed to enable the separation of presentation and content.
If HTML is like lumber, then CSS is interior decorating.
Why CSS?
Separating the style of a webpage from it’s content is very important. When tags like <font>, and color attributes were added to HTML 3 (we’re currently on HTML 5), it increased the possibilites for styling a web site without using CSS, but it was a nightmare for web developers. Development of large websites, where fonts and color information were added to every single page, became a long and arduous process.
Avoid duplication.
If you add style attributes to each HTML element you would have to write the same styles over and over again.
<font color="red" face="Verdana, Geneva, sans-serif" size="+1">This is my first paragraph.</font>
<font color="red" face="Verdana, Geneva, sans-serif" size="+1">This is my second paragraph.</font>
With CSS you can write something like the following, and it will apply to all of your <p> that include that style:
CSS
p{
color: red;
font-family: Arial;
font-size: 16px;
}
More attributes
The old style attributes and tags were limited to a few properties like color, font, font size, width, height, and a few others. Modern CSS now has ~520 properties and counting.
Smaller file size
Including a CSS style sheet allows your broswer to cache the file at the beginning of your session instead of loading all this markup each page load.