As you might have learned in a previous course, a Web page is made up of

three different layers that work together to deliver an experience to the user.

There's a content [SOUND] layer, a presentation layer, and

a behavior [SOUND] layer.

While [SOUND] HTML provides the content layer, and

the [SOUND] behavior layer is normally handled by JavaScript for real-time user

interaction, CSS is what handles the presentation layer of a Web page.

It's what makes our HTML look pretty.

[SOUND] You see, back in the early days of the Web before CSS was introduced,

developers would have to [SOUND] embed presentational tags and

attributes into HTML to control the design of a Web page.

And many of those tags were proprietary tags that only worked for

certain browsers, usually for the browser vendors that created them.

So, providing support and

maintaining a consistent look for every browser was nearly impossible.

Remember, HTML was never intended to be a presentation language, so

it made it difficult and impractical to create Web sites where the content of

each HTML page was separate from the presentation.

Imagine having to manually edit tens or

hundreds of HTML files to make a single styling change.

So there had to be a more efficient way of doing this, right?

Well, because of all the problems that came with this sort of

ad hoc way of styling Web pages,

CSS was finally introduced in HTML4 to help solve many of these problems.

With CSS, web authors finally had a way to express their designs without having to

add new HTML tags.

And by separating the content from the presentation,

[SOUND] CSS made the development and

maintenance of Web sites more efficient [SOUND] because the styles written in

a single CSS file could be [SOUND] shared across multiple Web pages.

Now, over the years, [SOUND] CSS has also improved the accessibility of web

content because it's allowed us to adapt our content to [SOUND] various devices,

[SOUND] screen sizes, and resolutions.

And what's exciting is that CSS continues to evolve.

As you'll soon learn, today's CSS features are becoming closer to

tools we'd normally use in a graphics editor like Photoshop.

That's because CSS3, the latest evolution of CSS,

has introduced many in-browser design features like rounded corners,

box shadows, gradients, animations, as well as new layout features like Flexbox.

So, us designers and developers now have more power and

flexibility when designing and building for the web.

It's a great time to be learning CSS.