Can You Set A Border Opacity In CSS?

Answer :

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);     -webkit-background-clip: padding-box; /* for Safari */     background-clip: padding-box; /* for IE9+, Firefox 4+, Opera, Chrome */ } 

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);     -webkit-background-clip: padding-box; /* for Safari */     background-clip: padding-box; /* for IE9+, Firefox 4+, Opera, Chrome */ } 

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).

UPDATE: I've added "background-clip: padding-box;" to this answer (per SooDesuNe's suggestion in the comments) to ensure the border remains transparent even if a solid background color is applied.

It's easy, use a solid shadow with 0 offset:

#foo {   border-radius: 1px;   box-shadow: 0px 0px 0px 8px rgba(0,0,0,0.3);        } 

Also, if you set a border-radius to the element, it gives you pretty rounded borders

jsFiddle Demo

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.