JSFiddle - React, Tailwind, and code Playground

HTML

<div id="mainHeaderTest">
	<ul>
	<li><span class="container1"><span class="diffLetter">Test</span>Header1</span></li>
	<li><span class="container2"><span class="diffLetter">Test</span>Header2</span></li>
	<li><span class="container3">Test<span class="diffLetter">Header3</span>en</span></li>
	<li><span class="container4"><span class="diffLetter">Test</span>Header4</span></li>
	<ul>
</div>

CSS

#mainHeaderTest li:hover .diffLetter {
  color: #BAB722
}