JSFiddle - React, Tailwind, and code Playground

HTML

<span class="font" id="size1">赤フォント</span><br />
<span>赤フォント</span class="font" id="size2">

CSS

.font{
	color:red;
}
#size1{
	font-size:30px;
}
#size2{
	font-size:30px;
}