JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
    <div class="child header"></div>
    <div class="child body">
        this content should fill up the parent and you should not see any black, nor should the body overflow the parent
    </div>
</div>

CSS

.parent {
    position:absolute;
    top:15px;
    left:15px;
    height:200px;
    width:200px;
    background:black;
}

.child {
    position:relative;
    color:white;
}

.header {
    height:25px;
    background:red;
}
.body {
   background:blue;   
}
}