CSS3 Border Opacity?

Question

Is there a straight forward way to make the border of an element semi-transparent with something like say

border-opacity:0.7;

?

If not anyone have an idea how i could do so without using images?

Answer 1

not as far as i know there isn't what i do normally in this kind of circumstances is create a block beneath with a bigger size((bordersize*2)+originalsize) and make it transparent using

filter:alpha(opacity=50);
-moz-opacity:0.5;
-khtml-opacity: 0.5;
opacity: 0.5;

here is an example
#main{
    width:400px;
    overflow:hidden;
    position:relative;
}
.border{
width:100%;
position:absolute;
height:100%;
background-color:#F00;
filter:alpha(opacity=50);
-moz-opacity:0.5;
-khtml-opacity: 0.5;
opacity: 0.5;

}
.content{
    margin:15px;/*size of border*/
    background-color:black;
}
<div id="main">
    <div class="border">
    </div>
    <div class="content">
    testing
    </div>
</div>

Answer 2

Unfortunately the opacity element makes the whole element (including any text) semi-transparent. The best way to make the border semi-transparent is with the rgba color format. For example, this would give a red border with 50% opacity:

div {
    border: 1px solid rgba(255, 0, 0, .5);
}

The problem with this approach is that some browsers do not understand the rgba format and will not display any border at all if this is the entire declaration. The solution is to provide two border declarations. The first with a fake opacity, and the second with the actual. If a browser is capable, it will use the second, if not, it will use the first.

div {
    border: 1px solid rgb(127, 0, 0);
    border: 1px solid rgba(255, 0, 0, .5);
}

The first border declaration will be the equivalent color to a 50% opaque red border over a white background (although any graphics under the border will not bleed through).

Answer 3

As others have mentioned: CSS-3 says that you can use the rgba(...) syntax to specify a border color with an opacity (alpha) value.

here's a quick example if you'd like to check it.

• It works in Safari and Chrome (probably works in all webkit browsers).

• It works in Firefox

• I doubt that it works at all in IE, but I suspect that there is some filter or behavior that will make it work.

There's also this stackoverflow post, which suggests some other issues--namely, that the border renders on-top-of any background color (or background image) that you've specified; thus limiting the usefulness of border alpha in many cases.