JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="main"></div>
  <div class="sidebar"></div>  
</div>

CSS

.container{
  background-color: #fff;
  font-size: 0;
}
.main,
.sidebar{
  display: inline-block;
  vertical-align: top;
}
.main{
  background-color: skyblue;
  width: 200px;
  height: 200vh;
}
.sidebar{
  background-color: tomato;
  width: 100px;
  height:110vh;
  position: sticky;
  bottom: 15px;
}