JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <div class="container">
    <div>
      <div>
       Some content Some content Some content Some content Some content Some content Some content Some content Some content Some content Some content Some 
      </div>
      <div class="fixed">
        Other content
      </div>
    </div>
  </div>
</div>

CSS

.container {
  width: 100%;
  height: 100%;
  position: absolute;
}

.container > div {
    width: 340px;
    overflow-y: auto;
    overflow-x: hidden;
    height: calc(100% - 50px);
    border: 1px solid red;
}

.container > div > .fixed {
    padding: 10px;
    position: fixed;
    bottom: 0;
    background-color: white;
    border: 1px solid green;
    width: inherit;
    box-sizing:border-box;
}