SOURCE

 <div class="box">
        <div class="box2"></div>
    </div>

     .box {
            border: 1px solid #f00;
            width: 500px;
            height: 500px;
            margin: auto;
        }
        .box2 {
            position: absolute;
            margin: auto;
            left: 0;
            top: -100px;
            bottom: 0;
            right: 0;
            border: 1px solid #00ff00;
            width: 100px;
            height: 100px;
        }