.block {

  box-sizing: border-box;

  width: 33.3%;

  height: 60px;

  padding: 0 5px 0 5px;

  display: inline-block;

  border: none;

  margin: none;

}

​

.block:first-child {

  padding-left: 10px;

}

.block:last-child {

  padding-right: 10px;

}

​

.inner {

  padding: 4px;

  border: 1px solid black;

}

.gutter {

  position: absolute;

}

.outer {

  border: 1px solid grey;

  padding: 10px 0 0 0;

}