How to Make The Background Div Only Transparent Using CSS

How to make div background color transparent in CSS

Opacity gives you translucency or transparency. See an example Fiddle here.

-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";       /* IE 8 */
filter: alpha(opacity=50);  /* IE 5-7 */
-moz-opacity: 0.5;          /* Netscape */
-khtml-opacity: 0.5;        /* Safari 1.x */
opacity: 0.5;               /* Good browsers */

Note: these are NOT CSS3 properties

See http://css-tricks.com/snippets/css/cross-browser-opacity/

CSS opacity only to background color, not the text on it?

It sounds like you want to use a transparent background, in which case you could try using the rgba() function:

rgba(R, G, B, A)
R (red), G (green), and B (blue) can be either <integer>s or <percentage>s, where the number 255 corresponds to 100%. A (alpha) can be a <number> between 0 and 1, or a <percentage>, where the number 1 corresponds to 100% (full opacity).
RGBa example
background: rgba(51, 170, 51, .1)    /*  10% opaque green */ 
background: rgba(51, 170, 51, .4)    /*  40% opaque green */ 
background: rgba(51, 170, 51, .7)    /*  70% opaque green */ 
background: rgba(51, 170, 51,  1)    /* full opaque green */ 

A small example showing how rgba can be used.

As of 2018, practically every browser supports the rgba syntax.

How to make the background DIV only transparent using CSS

Fiddle: http://jsfiddle.net/uenrX/1/

The opacity property of the outer DIV cannot be undone by the inner DIV. If you want to achieve transparency, use rgba or hsla:

Outer div:

background-color: rgba(255, 255, 255, 0.9); /* Color white with alpha 0.9*/

Inner div:

background-color: #FFF; /* Background white, to override the background propery*/

EDIT

Because you've added filter:alpha(opacity=90) to your question, I assume that you also want a working solution for (older versions of) IE. This should work (-ms- prefix for the newest versions of IE):

/*Padded for readability, you can write the following at one line:*/
filter: progid:DXImageTransform.Microsoft.Gradient(
    GradientType=1,
    startColorStr="#E6FFFFFF",
    endColorStr="#E6FFFFFF");

/*Similarly: */
filter: progid:DXImageTransform.Microsoft.Gradient(
    GradientType=1,
    startColorStr="#E6FFFFFF",
    endColorStr="#E6FFFFFF");

I've used the Gradient filter, starting with the same start- and end-color, so that the background doesn't show a gradient, but a flat colour. The colour format is in the ARGB hex format. I've written a JavaScript snippet to convert relative opacity values to absolute alpha-hex values:

var opacity = .9;
var A_ofARGB = Math.round(opacity * 255).toString(16);
if(A_ofARGB.length == 1) A_ofARGB = "0"+a_ofARGB;
else if(!A_ofARGB.length) A_ofARGB = "00";
alert(A_ofARGB);

Can I set an opacity only to the background image of a div?

Nope, this cannot be done since opacity affects the whole element including its content and there's no way to alter this behavior. You can work around this with the two following methods.

Secondary div

Add another div element to the container to hold the background. This is the most cross-browser friendly method and will work even on IE6.

HTML

<div class="myDiv">
    <div class="bg"></div>
    Hi there
</div>

CSS

.myDiv {
    position: relative;
    z-index: 1;
}

.myDiv .bg {
    position: absolute;
    z-index: -1;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    background: url(test.jpg) center center;
    opacity: .4;
    width: 100%;
    height: 100%;
}

See test case on jsFiddle

:before and ::before pseudo-element

Another trick is to use the CSS 2.1 :before or CSS 3 ::before pseudo-elements. :before pseudo-element is supported in IE from version 8, while the ::before pseudo-element is not supported at all. This will hopefully be rectified in version 10.

HTML

<div class="myDiv">
    Hi there
</div>

CSS

.myDiv {
    position: relative;
    z-index: 1;
}

.myDiv:before {
    content: "";
    position: absolute;
    z-index: -1;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    background: url(test.jpg) center center;
    opacity: .4;
}

Additional notes

Due to the behavior of z-index you will have to set a z-index for the container as well as a negative z-index for the background image.

Test cases

See test case on jsFiddle:

Using CSS 2.1 :before
Using CSS 3 ::before

CSS: opacity only background, not the text inside

The easy way would be to move the text into a separate div, like so. Basically you apply the opacity to a separate div and position the text on top...

<div id="parent">
   <div id="opacity"></div>
   <div id="child">text</div>
</div>

div#parent { position:relative; width:200px; height:200px; }
div#child { position:absolute; width:200px; height:200px; z-index:2; }
div#opacity { position:absolute; width:200px; height:200px; z-index:1; }

The other route would be rgba. Don't forget there's a separate css property to feed IE since it doesn't support the rgba property. You can also feed a transparent png.

#regForm {
   background: rgb(200, 54, 54); /* fallback color */
   background: rgba(200, 54, 54, 0.5);
}

And for IE...

<!--[if IE]>

   <style type="text/css">

   .color-block {
       background:transparent;
       filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#99000050,endColorstr=#99000050);
       zoom: 1;
    } 

    </style>

<![endif]-->

Personally I'd go with the first option because it's less of a hassle.

How to make a div's background color translucent?

You can use the background-color: rgba() notation:

#theIdofYourElement,
.classOfElements {
    background-color: #fff;
    background-color: rgba(255,255,255,0.5);
}

Edited to add the default background-color (for browsers that don't understand the rgba() notation). Albeit I was under the impression that all but IE do understand it (but I could be wrong, and haven't tested to be sure...).

Edit with thanks to @akamike.

Edited to address question from OP (in comments):

which browsers don't understand rgba? will they all in the future, is this part of css3?

The best information I could find is the CSS Tricks' rgba() browser support table, with a link to a demo and 'more complete' compatibility table.

CSS Background Opacity

Children inherit opacity. It'd be weird and inconvenient if they didn't.

You can use a translucent PNG file for your background image, or use an RGBa (a for alpha) color for your background color.

Example, 50% faded black background:

<div style="background-color:rgba(0, 0, 0, 0.5);">   <div>      Text added.   </div></div>

Opacity of div's background without affecting contained element in IE 8?

The opacity style affects the whole element and everything within it. The correct answer to this is to use an rgba background colour instead.

The CSS is fairly simple:

.myelement {
    background: rgba(200, 54, 54, 0.5);
}

...where the first three numbers are the red, green and blue values for your background colour, and the fourth is the 'alpha' channel value, which works the same way as the opacity value.

See this page for more info: http://css-tricks.com/rgba-browser-support/

The down-side, is that this doesn't work in IE8 or lower. The page I linked above also lists a few other browsers it doesn't work in, but they're all very old by now; all browsers in current use except IE6/7/8 will work with rgba colours.

The good news is that you can force IE to work with this as well, using a hack called CSS3Pie. CSS3Pie adds a number of modern CSS3 features to older versions of IE, including rgba background colours.

To use CSS3Pie for backgrounds, you need to add a specific -pie-background declaration to your CSS, as well as the PIE behavior style, so your stylesheet would end up looking like this:

.myelement {
    background: rgba(200, 54, 54, 0.5);
    -pie-background:  rgba(200, 54, 54, 0.5);
    behavior: url(PIE.htc);
}

Hope that helps.

[EDIT]

For what it's worth, as others have mentioned, you can use IE's filter style, with the gradient keyword. The CSS3Pie solution does actually use this same technique behind the scenes, but removes the need for you to mess around directly with IE's filters, so your stylesheets are much cleaner. (it also adds a whole bunch of other nice features too, but that's not relevant to this discussion)

How to make opacity only for background?

Hi if your background does not has any Images.
Then easily you can apply opacity on it background.
Here is some example you can use ->

background-color: #00ff0055;
/*-- The value after six digit is your alpha color or opacity of background.--*/
background-color: #0f05; /*-- Same as previous one.--*/
background-color: rgba(0,255,0,.5); /*-- a extend for alpha color--*/

Hope this help you.

Making div element background transparent to background image CSS

If you want to set the background color to transparent you can do all of these.

background-color: ; background-color: transparent; background-color: rgba(0, 0, 0, 0);

but in this case, you need to set a different position here is the code I hope this is what you were looking for

<div style="height:100px;font-size:36px; border:1px solid red; position: absolute;">
  Some text goes here, need to try to make the background of this transparent? Any ideas?
</div>