JSFiddle - React, Tailwind, and code Playground

by extempl

HTML

<div class="parent">
   <div class="child child1"> I want to set the width of this element equals to its height (which is equals to the height of the content of it's  sibling, set by `align-items : stretch`) </div>
   <div class="child childs-sibling">
          some text <br>
          some text <br>
          some text <br>
          some text <br>
   </div>
</div>

CSS

.parent {
    display: flex;
    align-items: stretch;
    height:200px;
}

.parent .child {
    border: 1px solid black;
    flex:auto;
    flex-basis: 100%;
}

.parent .child1 {
  flex-basis: 200px;
  min-width: 200px;
}