html {
height:100%;
}
body {
margin:0;
height:100%;
display: flex;
}
.a, .b {
flex:1;
position: relative;
}
.a {
border-right:2px solid;
}
.c {
border:2px solid;
position: absolute;
height: 200px;
width: 200px;
left: 50%;
transform:translate(-50%,-50%);
top:50%;
}
.d {
position: absolute;
left: 50%;
transform:translateX(-50%);
top:20px;
width: 80%;
height: 70px;
border:2px solid;
}
<div class="a">
<div class="c"></div>
</div>
<div class="b">
<div class="d"></div>
</div>