JSFiddle - React, Tailwind, and code Playground

by bizamajig

HTML

<div class="conversation">
  <div class="messages-container">
    <div class="scroll">
      <p>Message 1<p>Message 2<p>Message 3<p>Message 4<p>Message 5
      <p>Message 6<p>Message 7<p>Message 8<p>Message 9<p>Message 10
    </div>
  </div>
  <textarea class="text-input" autofocus>Your message</textarea>
  <div>
    <button id="send" onclick="send();">Send input</button>
    <button id="resize" onclick="resize();">Resize input box</button>
  </div>
</div>

CSS

html,body {height: 100%;margin: 0;}
.conversation {
  display: flex;
  flex-direction: column;
  height: 100%;
}
.messages-container {
  flex-shrink: 10;
  height: 100%;
  overflow: auto;
}
.messages-container, .scroll {transform: scale(1,-1);}
.text-input {resize: vertical;}

JavaScript

//Reverse wheel direction
document.querySelector('.messages-container').addEventListener('wheel', function(e) {
  if(e.deltaY) {
    e.preventDefault();
    e.currentTarget.scrollTop -= parseFloat(getComputedStyle(e.currentTarget).getPropertyValue('font-size')) * (e.deltaY < 0 ? -1 : 1) * 2;
  }
});

//The rest of the JS just handles the test buttons and is not part of the solution
send = function() {
  var inp = document.querySelector('.text-input');
  document.querySelector('.scroll').insertAdjacentHTML('beforeend', '<p>' + inp.value);
  inp.value = '';
  inp.focus();
}
resize = function() {
  var inp = document.querySelector('.text-input');
  inp.style.height = inp.style.height === '50%' ? null : '50%';
}