JSFiddle - React, Tailwind, and code Playground

HTML

<div>
<span class="a">something</span>
<span class="b">fill the rest</span> 
</div>

<div>
<span class="a">something</span>
<input class="b" value="fill the rest">       
</div>

CSS

.a {
    float:left; background-color:red
}
.b {
    background-color:green;display:block;
}