CSS

The Opacity Property is slightly different then RGBA and HSLA which was discussed in CSS3 Colors.

Opacity v. RGBA & HSLA

Indeed RGBA has the addition of the “alpha” or opacity value like so:

background-color:rgba(127, 60, 87, 0.4);
background-color:hsla(68, 100%, 50%, 0.8);

Either of these examples will have a color that is opaque in some fashion. Consider the following:

If you’re using IE see below:

background-color:rgba(0, 0, 255, 1);
background-color:rgba(0, 0, 255, 0.8);
background-color:rgba(0, 0, 255, 0.6);
background-color:rgba(0, 0, 255, 0.4);
background-color:rgba(0, 0, 255, 0.2);

This code using rgba allows us to create our desired effect.

Allows us to use these opaque colors, however, we can reach the same effect using the standard rgb color space or by using hexadecimal values.

Consider the following example:

We have the same effect using slightly different code in fact. We used the opacity property to create the fading squares.

background-color:rgb(0, 0, 255); opacity:1.0;
background-color:rgb(0, 0, 255); opacity:0.8;
background-color:rgb(0, 0, 255); opacity:0.6;
background-color:rgb(0, 0, 255); opacity:0.4;
background-color:rgb(0, 0, 255); opacity:0.2;

Main difference

The main difference between rgba + hsla and opacity is that we can apply opacity to any element we want instead of just backgrounds. This includes, but is not limited to, images and text.

As we can see, the text is fading with word. The first word is at 100% opacity, the second at 80%, third at 60%, etc… We denote these values in terms of decimals so 1 = 100%, 0.8 = 80%, etc…

Opacity

One really great thing about the opacity property is that you don’t need to create an image sprite if you want an image to be slightly translucent before roll over and fully opaque during roll over. Here is an example of opacity:

.chrome-opacity {
  background:url (images/chrome.png) center center no-repeat;
  height:64px;
  width:64px;
  opacity:0.8;
}
.chrome-opacity:hover {
  background:url (images/chrome.png) center center no-repeat;
  height:64px;
  width:64px;
  opacity:1.0;
}

Using method above allows us to easily create semi-opaque images or text and allow them to become fully opaque on roll over or vice versa.

Note: IE 6 only supports the :hover pseudo-class on <a> tags only. Also, IE does not natively support this property where all of the other major browsers do.

To use this property with IE we’ll need to create a conditional comment for all versions of IE like the following:

<!--[if IE]>
   <style type="text/css">
        .chrome {filter:alpha(opacity=80);}
	.chrome:hover {filter:alpha(opacity=100);}
   </style>
<![endif]-->

Note: that IE 6 and 7 do NOT extend support to the pseudo-class :hover on anything but <a> tags and therefore the hover will not work.

If you want to see working examples of the opacity property then please download the file!

opacity.zip
Size: 170.97 KB

You might be wondering what is so special about CSS3 colors and why they’re even different considering that the color and background-color property and their values have not changed since CSS1 specification were released.

As set by CSS1 we can use the following for the color and background-color properties:

Aside from these standard mundane implementations of colors, CSS3 added a whole new color space: HSL.

HSL

HSL stands for Hue Satuation and Lightness. The break down is as follows:

Here is an example of HSL:

Here is an example with RGB:

Here is an example with HEX:

The corresponding CSS for HSL colors is the following:

background-color:hsl ([0-360], [x]%,[x]%);
background-color:hsl (360, 100% 50%);
background-color:hsl (133,85%, 61%);

RGBA

There is nothing new about the RGB color space. We learned about the RGB color space in Basics of CSS Part 2 and we have seen many colors in the RGB color space and in hex format Color Reference.

Common examples of RGB would be the following:

background-color:rgb(255, 0, 0); /*red*/
background-color:rgb(0, 255, 0); /*green*/
background-color:rgb(0, 0, 255); /*blue*/

So what does the “a” mean in RGBA? The A stands for alpha which deals with transparency or the opacity of colors. The syntax for the alpha value will span from 0-1 in decimal form. For example:

background-color:rgba(0, 0, 255, 0.4);
color:rgba(0, 0, 255, 0.8);

The first example will set the opacity of pure blue to 40% and the second example will set the opacity of pure blue to 80%.

Alternatively, the RGB colors will be the following:

For example

Notice how above they were the same colors and now since we have a different color background the colors with rgba will allow the black background to show through where as the rgb colors will display their respective color values.

Which Browsers Support RGBA?

• Firefox 3.x+
• Safari 3+
• Safari 4+
• Google Chrome
• Opera 10.10+
• Flock 2.02
• Mobile Safari
• Blackberry Browser

IE Hack

Mission someone? Of course we are! We’re missing lovely Internet Explorer and all of its versions. Luckly, there is a hack for IE.

<!--[if IE]>
   <style type="text/css">
   selector {
       background:transparent;
       filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#990000FF,endColorstr=#990000FF);
    }
    </style>
<![endif]-->

We can use this hack as inline css or use in an internal or external style sheet. If you want a specific class selector or element to have an translucent color then use the hack for that element or class like the example above. If you want to use inline css then place the hack in the style attribute.

You might be wondering what #800000FF is. Think of this as #AARRGGBB where AA is the alpha value in two integers, RR are the red hexadecimals, GG are the green hexadecimals, and BB are the blue hexadecimals.

In order to covert our initial RGBA value to Hex we need to think interms of Hex to Decimal values.

Hex to Decimal

In order to convert Hex to Decimal we need to think mathematically. We’ll start with an easy example:

How did we get these values of the top of our head? The solution is simple. Follow these steps from Jackson Hines’s post on RGB to HEX and vice versa:

HEX to RGB (Ex: #a84fff)

1. Take the first digit of the red part of the hex color. (ex: a)
2. If this digit is a letter, replace with the letter of the alphabet and add 9. If it is not a letter, leave it. (ex: a = 1; 1 + 9 = 10)
3. Take the second digit of the red part of the hex color. (ex: 8 )
4. If this digit is a letter, replace with the letter of the alphabet and add 9. If it is not a letter, leave it. (ex: 8 )
5. Divide this number by 16. (ex: 8 ÷ 16 = 0.5)
6. Add the number you got in step two and the number you got in step 5. (ex: 10 + 0.5 = 10.5)
7. Multiply this number by 16 to get the red value. (ex: 10.5 × 16 = 168)
8. Repeat steps 1 through 8 with green and blue values. (ex: 168, 79, 255))

Alpha (#AA) & A

So what about alpha? Knowing the information we have obtained by Jackson’s helpful article, we can convert our rgb value to hex and vice versa. If you wish not to do so much math and want to get results quickly, I recommend using Colorpicker.com.

#AARRGGBB to RGBA

Let us assume #660000FF is our #AARRGGBB color of choice. Convert #0000FF to RGB which will be rgb(0, 0, 255) and now time to convert #AA.

Following HEX to RGB conversion of #66:

1. The first number is 6
2. The second number is 6 ÷ 16 = 0.375
3. The third number is the (first number + the second number) × 16 = 102
4. 102 ÷ 255 = 0.4 for RGBA

If you don’t want to that much math then you can use this conversion tool to convert any TWO hex characters to decimal or any series of Decimal characters. Once you have your decimal number, divide by 255 and you will have your RGBA number.

HSLA

Using the same principles as RGBA and HSL, just add the A to the end of the HSL values. For example

background-color:hsla ([0-360], [x]%, [x]%, [0-1]);
background-color:hsla (133, 85%, 61%, 0.6);

For more information an examples on the IE Hack for RGBA and HSLA, please download css3-colors.zip and open in IE.

css3-colors.zip
Size: 1.71 KB