Two color borders

Solution 1:

Yep: Use the outline property; it acts as a second border outside of your border. Beware, tho', it can interact in a wonky fashion with margins, paddings and drop-shadows. In some browsers you might have to use a browser-specific prefix as well; in order to make sure it picks up on it: -webkit-outline and the like (although WebKit in particular doesn't require this).

This can also be useful in the case where you want to jettison the outline for certain browsers (such as is the case if you want to combine the outline with a drop shadow; in WebKit the outline is inside of the shadow; in FireFox it is outside, so -moz-outline: 0 is useful to ensure that you don't get a gnarly line around your beautiful CSS drop shadow).

.someclass {
  border: 1px solid blue;
  outline: 1px solid darkblue;
}

Edit: Some people have remarked that outline doesn't jive well with IE < 8. While this is true; supporting IE < 8 really isn't something you should be doing.

Solution 2:

This is very possible. It just takes a little CSS trickery!

div.border {
  border: 1px solid #000;
  position: relative;
}

div.border:before {
  position: absolute;
  display: block;
  content: '';
  border: 1px solid red;
  height: 100%;
  width: 100%;
  box-sizing: border-box;
  -moz-box-sizing: border-box;
  -webkit-box-sizing: border-box;
}

<div class="border">Hi I have two border colors<br />I am also Fluid</div>

Is that what you are looking for?

Solution 3:

Another way is to use box-shadow:

#mybox {
box-shadow:
  0 0 0 1px #CCC,
  0 0 0 2px #888,
  0 0 0 3px #444,
  0 0 0 4px #000;
-moz-box-shadow:
  0 0 0 1px #CCC,
  0 0 0 2px #888,
  0 0 0 3px #444,
  0 0 0 4px #000;
-webkit-shadow:
  0 0 0 1px #CCC,
  0 0 0 2px #888,
  0 0 0 3px #444,
  0 0 0 4px #000;
}

<div id="mybox">ABC</div>

See example here.