<!DOCTYPE HTML>
<style>
body {
    margin: 0;
}
div {
    width: 50%;
    height: 100px;
    position: absolute;
    background-color: green;
    border: blue solid 20px;
}
.border-box {
    box-sizing: border-box;
}
.content-box {
    box-sizing: content-box;
}
</style>
<div id="target1" class="content-box" style="top: 0px"></div>
<div id="target2" class="border-box" style="top: 200px"></div>