JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
    

    <div class="child1">
                 I want the parent to be as tall as the two children divs.
    </div>
    
    <div class="child2">
        You can see where the parent div ends 
        
    </div>
</div>

CSS

html, body { width: 100%; height: 100%; }

.parent {
    width: 100%;
    height: 100%;
    position: relative;
    background: #CCC;
}

.child1 {
    width: 100%;
    height: 100%;
    min-height: 300px;
    max-height: 600px;
    background: #DDD;
}

.child2 {
    width: 100%;
    height: 1500px;
    background: rgba(0, 0, 0, 0.3);
}