JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="top-area">
        <p>we have some text here, or UI controls</p>
        <p>that might increase in length (affecting the height)</p>
        <p>thus this area should affect the bottom-area</p>
        <p>this should also be non-scrollable</p>
    </div>
    
    <div class="bottom-area">
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
        <p>lots of data</p>
    </div>
</div>

CSS

.container{
    position: absolute;
    top: 30px;
    right: 30px;
    bottom: 30px;
    left: 30px;
    background: #05bdf2;
    border: 2px solid black;
    
    display: flex;
    flex-direction: column;
}

.top-area{
    background: red;
    /* overflow: hidden; */
}

.bottom-area{
    height: 0;
    flex-grow: 1;
    overflow: auto;

}