Question

Is it possible to draw an arrow that has semi-transparent border around it just using css?

Heres a fiddle of my effort so far:
http://jsfiddle.net/calebo/fBW4u/

CSS:

.ui-overlay {
  padding-bottom: 10px;   
  position: relative;
}
.ui-overlay-content { 
  background: #999;
  color: #000;
  padding: 8px;
  border-radius: 4px; 
  border: 5px solid rgba(0, 0, 0, 0.2); 
  background-clip: padding-box; 
  height: 100px;
  width: 200px;
}
.arrow {
  border-color: #999 transparent transparent; 
  border-style: solid; 
  border-width: 10px 10px 0; 
  bottom: 5px; 
  left: 15px; 
  width: 0;
  height: 0;
  position: absolute;
  overflow: hidden; 
}

Answer 1

This still needs some work, but here’s the general idea:

Use a pseudo-element, rotate it 45deg and apply the styling to that:

.arrow {
    bottom: -25px; 
    left: 30px; 
    width: 40px;
    height: 40px;
    position: absolute;
    overflow: hidden;
}
.arrow:after {
    content: ' ';
    display: block;
    background: red;
    width: 20px;
    height: 20px;
    transform: rotate(45deg);
    position: absolute;
    top: -19px;
    left: 3px;
    background: #999;
    border: 5px solid rgba(0, 0, 0, 0.2);
    background-clip: padding-box;
}

Here’s the fiddle: http://jsfiddle.net/yZ3vB/

---

The problem with this is that the borders overlap, making it darker by the edges.

This could probably be remedied by adding another element though.

Update: Yes! Here you go: http://jsfiddle.net/sJFTT/

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Update 2: You don’t even need that additional element. You can use the pseudo element from the main box:

.ui-overlay-content:after {
    content: ' ';
    border-width: 13px;
    border-color: #999 transparent transparent;
    border-style: solid;
    bottom: -10px;
    left: 30px;
    width: 0;
    height: 0;
    position: absolute;
}

Here’s the fiddle: http://jsfiddle.net/6v9nV/

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Update 3: Actually, you can do all this with just a single element and no transform, by using both pseudo-elements – the before and the after:

.speech-bubble {
    background: #999;
    background: linear-gradient(top, #444 0%,#999 100%);
    background-clip: padding-box;
    border: 5px solid rgba(0, 0, 0, 0.2);
    padding: 20px;
    width: 200px;
    height: 100px;
    position: relative;
}
.speech-bubble:before{
    content: ' ';
    border-color: rgba(0, 0, 0, 0.2) transparent transparent;
    border-style: solid;
    border-width: 17px;
    position: absolute;
    bottom: -39px;
    left: 16px;
}
.speech-bubble:after{
    content: ' ';
    border-color: #999 transparent transparent;
    border-style: solid;
    border-width: 13px;
    position: absolute;
    bottom: -26px;
    left: 20px;
}

Here’s the fiddle: http://jsfiddle.net/95vvr/

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P.S. Don’t forget the vendor prefixes in production!