.parent{
    border: 1px solid #aaa;
    position: relative;
    height: 200px;
    width: 300px;
}
.inner{
    width: 450px;
    height: 450px;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    position: absolute;
    margin: auto;
}