JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.21/themes/base/jquery-ui.css">
<div id="main">
    <div id="first">
        <div id="first-head">
             <h3>First</h3>

        </div>
        <div id="first-body">
            <p>First-1</p>
            <p>First-2</p>
            <p>First-3</p>
            <p>First-4</p>
            <p>First-5</p>
            <p>First-6</p>
             
        </div>
    </div>
    <div id='second'>
        <div id="second-head">
             <h3>Second</h3>

            <div class="ui-resizable-handle ui-resizable-s" id="ngrip"></div>
        </div>
        <div id="second-body">
            <p>Second-1</p>
            <p>Second-2</p>
            <p>Second-3</p>
            <p>Second-4</p>
            <p>Second-5</p>
            <p>Second-6</p>
            <p>Second-1</p>
            <p>Second-2</p>
            <p>Second-3</p>
            <p>Second-4</p>
            <p>Second-5</p>
            <p>Second-6</p>
        </div>
    </div>
</div>

CSS

#main {
    width:100%;
    height:400px;
   
}
#first, #second {
    min-height:100px;
    height:170px;
    max-height:400px;
   
  
}
#second-body{
   z-index:9999;
}
#first-head, #second-head {
    background-color:red;
    
}
#first-body {
    overflow-y:auto;
    height:100%;
     margin-bottom:10px;
}
#second-body
{
 overflow-y:auto;
    height:100%;
     margin-bottom:10px;
}
#ngrip {
        position: absolute;
    width: 10px;
    height: 10px;
    background-color: #ffffff;
    border: 1px solid #000000;
top:0px;
    left: 50%;
}

JavaScript

$('#second').resizable({
    handles: {
        'n': '#ngrip',
    },
    resize: function () {
        
        var b = $('#second').height();
        var height=$('#main').height();
        var a = $('#first').css("height", b + "px");
        var first=$('#first').height();
        $('#second').css("height",height- first+ "px");
        console.log(a.height());
    }
});