Edit in JSFiddle

.box{
    margin:40px;
    height:200px;
    position: relative;
    background:#e9e9e9;
    padding:40px;
}

.box:before{
    content: '';
    z-index: 1;
    position: absolute;
    border: 1px dashed #bbb;
    top: 7px;
    bottom: 7px;
    left: 7px;
    right: 7px;
    -moz-box-shadow: 0 0 0 1px #eee;
    -webkit-box-shadow: 0 0 0 1px #eee;
    box-shadow: 0 0 0 1px #eee;
}

<div class="box">こんな感じの縫い目線みたいなボックス作ったり</div>