How do I give text or an image a transparent background using CSS?

Question

Is it possible, using CSS only, to make the background of an element semi-transparent but have the content (text & images) of the element opaque?

I'd like to accomplish this without having the text and the background as two separate elements.

When trying:

p {
  position: absolute;
  background-color: green;
  filter: alpha(opacity=60);
  opacity: 0.6;
}

span {
  color: white;
  filter: alpha(opacity=100);
  opacity: 1;
}

<p>
  <span>Hello world</span>
</p>

Answer 1

Either use a semi-transparent PNG image or use CSS 3:

background-color: rgba(255, 0, 0, 0.5);

Here's an article from css3.info, Opacity, RGBA and compromise (2007-06-03).

<p style="background-color: rgba(255, 0, 0, 0.5);">
  <span>Hello, World!</span>
</p>

Answer 2

A little known trick is that you can use it in Internet Explorer as well using the gradient filter.

background-color: rgba(0, 255, 0, 0.5);
filter: progid:DXImageTransform.Microsoft.Gradient(GradientType=0, StartColorStr='#7F00FF00', EndColorStr='#7F00FF00');

The first hex number defines the alpha value of the color.

Full solution all browsers:

.alpha60 {
    /* Fallback for web browsers that doesn't support RGBa */
    background: rgb(0, 0, 0) transparent;
    /* RGBa with 0.6 opacity */
    background: rgba(0, 0, 0, 0.6);
    /* For IE 5.5 - 7*/
    filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#99000000, endColorstr=#99000000);
    /* For IE 8*/
    -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#99000000, endColorstr=#99000000)";
}

Answer 3

This is the best solution I could come up with, NOT using CSS 3. And it works great on Firefox, Chrome, and Internet Explorer as far as I can see.

Put a container div and two children divs at the same level, one for content, one for the background. And using CSS, auto-size the background to fit the content and put the background actually in the back using z-index.

.container {
  position: relative;
}
.content {
  position: relative;
  color: White;
  z-index: 5;
}
.background {
  position: absolute;
  top: 0px;
  left: 0px;
  width: 100%;
  height: 100%;
  background-color: Black;
  z-index: 1;
  /* These three lines are for transparency in all browsers. */
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";
  filter: alpha(opacity=50);
  opacity: .5;
}

<div class="container">
  <div class="content">
    Here is the content.
    <br/>Background should grow to fit.
  </div>
  <div class="background"></div>
</div>