JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
			<div class="child1">
				{SUBJECT}
			</div>
			<span class="child2">
				<button class="but"><i class="fa fa-user fa-fw" ></i></button>
			</span>
		</div>

CSS

.child1{
padding: 10px;	flex: 1;

}
.parent {
	font-size: 20px;
height: 50px;
border: 1px solid rgba(0, 0, 0, 0.125);
	display: flex;
}
.child2 {
	flex: 0;

}