.block1 {
height: 100vh;
background-color: chocolate;
position: relative;
z-index: 100;
}
.block2 {
height: 120vh;
background-color: aqua;
position: relative;
top: -150px;
z-index: 50;
}
.block3 {
height: 100vh;
background-color: chocolate;
position: relative;
top: -180px;
z-index: 100;
}
<body>
<div class="block1"></div>
<div class="block2"></div>
<div class="block3"></div>
</body>
.block3 {
height: 100vh;
background-color: chocolate;
position: relative;
top: -180px;
z-index: 100;
}