<!DOCTYPE html>
<style>
body {
   position: relative;
   height: 100vh;
}
.item1 {
   width: fit-content;
   margin: 0px auto;
}
.item2 {
   position: absolute;
   bottom: 0;
   background-color: cyan;
   height: 50px;
   width: 100%;
}
</style>
<div class="item1">item1</div>
<div class="item2">item2</div>