In the early days of the Internet, your tools for building a website were HTML and little else. But trying to design a site with nothing more than HTML can be tedious and limiting. This is where CSS comes in.
Cascading Style Sheets, also known as CSS, are files that tell the web browser how to display an HTML page. Basically, the HTML page serves as the skeleton, the basic framework of a web page, while the CSS document specifies how the specific elements of a page should look. CSS lets you control the fonts, font colours, background styles and so forth, of an HTML page.
CSS makes it easier to design and build a website. Before CSS, you had to use HTML to specify how all individual headers and components of a page looked and acted. While there were ways around this, HTML was often misused and the web developer would have to go in and individually change every page element on every page. CSS made it drastically less complex and less time consuming to change the styles on a web page. You could make the change to one document and apply the change across your entire site.
What's Next: HTML5 and CSS3
HTML5 and CSS3 are the latest of markup programming. HTML5’s video element, which simplifies adding video to a web page, has been getting all the attention, but HTML5 has many features that will put it ahead of the game and make it great for users and web developers alike.
Flash-free Video and Animation
HTML5 will allow you to watch videos without using a plugin like Flash or Silverlight.
So what’s the big deal with the new video feature of HTML5? Well for one, it’s free to use and doesn’t require the Adobe Flash plugin. Second, Flash may slow down your computer (though the hardware accelerated Flash 10.1, now in beta, should help matters, and Flash's impact will depend on your hardware and OS); it's one more piece of software running and eating up system resources, after all. With HTML5, the video feature is built right in.