Border Corners: Triangle

Question

Is it possible to get rid of the \"triangle\" shape in the border corners? (when using different color borders)

See this example:

http://jsfiddle.net/GLsqV/

Answer 1

Not everywhere with a single element. (Actually, the default triangular shape of borders is what makes great things possible: The Shapes of CSS)

However, what you are asking for is easily possible everywhere with another child element.

CSS:

.borders {
  width: 520px;
  height: 500px;
  border-top: 10px solid red;
  border-bottom: 10px solid green;
}

.borders2 {
  background: #efefef;
  width: 500px;
  height: 500px;    
  border-left: 10px solid black;
  border-right: 10px solid black;
}

​ HTML:

<div class="borders">
  <div class="borders2">
  </div>
</div>​

With these values, the outer DIV's border-box will still have a size of 520×520 pixels.

See also this fiddle.

Answer 2

One option using generated content:

.borders {
    width:500px;
    height:500px;
    position: relative;
    background:#efefef;
    border-top:10px solid red;
    border-bottom:10px solid green;
}

.borders::before,
.borders::after {
    content: '';
    position: absolute;
    width: 10px;
    top: 0;
    bottom: 0;
    background-color: #000;
}

.borders::before {
    left: 0;
}

.borders::after {
    right: 0;
}

JS Fiddle demo.

Or with nested HTML (if you really must):

<div class="borders">
    <div class="innerBorder left"></div>
    <div class="innerBorder right"></div>
</div>​

.borders {
    width:500px;
    height:500px;
    position: relative;
    background:#efefef;
    border-top:10px solid red;
    border-bottom:10px solid green;
}

.borders .innerBorder{
    content: '';
    position: absolute;
    width: 10px;
    top: 0;
    bottom: 0;
    background-color: #000;
}

.borders .left {
    left: 0;
}

.borders .right {
    right: 0;
}

JS Fiddle demo.

And a single-nested-element solution in which the left, and right, border-color is the background-color of the wrapping element, and the width controlled by the margin of the descendant:

<div class="borders">
    <div class="inner"></div>
</div>​

CSS:

.borders {
    width:500px;
    height:500px;
    background-color: #000;
    border-top:10px solid red;
    border-bottom:10px solid green;
}

.borders .inner {
    background-color: #efefef;
    height: 100%;
    margin: 0 10px;
}

JS Fiddle demo.​

Answer 3

That's how borders work. How would the browser decide which ones overlap the corners otherwise?

You can achieve this effect using a nested DIV, or using a trick with :before and :after with some absolute positioning.