JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flexbox">
  <div class="item-1">
      <span>I want to be aligned at the bottom of item-1</span>
  </div>

  <div class="item-2">
      <span>I want to be aligned at the bottom of item-2</span>
  </div>
</div>

CSS

div.flexbox {
  display: -webkit-flex;
  -webkit-align-items: stretch; /* cross axis */
  -webkit-justify-content: space-between; /* main axis */
  -webkit-flex-flow: row wrap;
  border-bottom: 1px solid #ddd;
  min-height: 200px;
  -webkit-align-items:flex-end;  
}

.item-1, .item-2 {
    padding: 10px;  
}

.item-1 {
  width: 30%;
  position: relative;  
}

.item-2 {
  width: 60%;
}