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_
}
_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>
_x000D_