[css] How to make borders collapse (on a div)?

Suppose I have markup like: http://jsfiddle.net/R8eCr/1/

<div class="container">
    <div class="column">
        <div class="cell"></div>
        <div class="cell"></div>
        <div class="cell"></div>
    </div>
    <div class="column">
        <div class="cell"></div>
        <div class="cell"></div>
        <div class="cell"></div>
    </div>
    <div class="column">
        <div class="cell"></div>
        <div class="cell"></div>
        <div class="cell"></div>
    </div>
    ...
</div>

Then CSS

.container {
    display: table;
    border-collapse: collapse;
}
.column {
    float: left;
    overflow: hidden;
    width: 120px;
}
.cell {
    display: table-cell;
    border: 1px solid red;
    width: 120px;
    height: 20px;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
}

I have the outer div with display: table; border-collapse: collapse; and cells with display: table-cell why do they still not collapse? What am I missing here?

By the way there maybe variable number of cells in a column so I can't only have borders on one side.

You could also use negative margins:

.column {_x000D_
  float: left;_x000D_
  overflow: hidden;_x000D_
  width: 120px;_x000D_
}_x000D_
.cell {_x000D_
  border: 1px solid red;_x000D_
  width: 120px;_x000D_
  height: 20px;_x000D_
  box-sizing: border-box;_x000D_
}_x000D_
.cell:not(:first-child) {_x000D_
  margin-top: -1px;_x000D_
}_x000D_
.column:not(:first-child) > .cell {_x000D_
  margin-left: -1px;_x000D_
}

<div class="container">_x000D_
  <div class="column">_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
  </div>_x000D_
  <div class="column">_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
  </div>_x000D_
  <div class="column">_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
  </div>_x000D_
  <div class="column">_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
  </div>_x000D_
  <div class="column">_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
    <div class="cell"></div>_x000D_
  </div>_x000D_
</div>

Use simple negative margin rather than using display table.

Updated in fiddle JS Fiddle

.container { 
    border-style: solid;
    border-color: red;
    border-width: 1px 0 0 1px;
    display: inline-block;
}
.column { 
    float: left; overflow: hidden; 
}
.cell { 
    border: 1px solid red; width: 120px; height: 20px; 
    margin:-1px 0 0 -1px;
}
.clearfix {
    clear:both;
}

Example of using border-collapse: separate; as

ol[type="I"]>li{
  display: table;
  border-collapse: separate;
  border-spacing: 1rem;
}

You need to use display: table-row instead of float: left; to your column and obviously as @Hushme correct your diaplay: table-cell to display: table-cell;

 .container {
    display: table;
    border-collapse: collapse;
}
.column {
    display: table-row;
    overflow: hidden;
    width: 120px;
}
.cell {
    display: table-cell;
    border: 1px solid red;
    width: 120px;
    height: 20px;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
}

demo

Instead using border use box-shadow:

  box-shadow: 
    2px 0 0 0 #888, 
    0 2px 0 0 #888, 
    2px 2px 0 0 #888,   /* Just to fix the corner */
    2px 0 0 0 #888 inset, 
    0 2px 0 0 #888 inset;

Demo: http://codepen.io/Hawkun/pen/rsIEp

Why not use outline? it is what you want outline:1px solid red;