JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="main_content"> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
            <p>long content</p> 
    </div> 
    <div id="side_content"> 
    Finally I am fixed here!!
    </div> 
</div>

CSS

body { padding: 0; }
#container {
    width: 500px;
    margin: 0 auto;
    position: relative;
    overflow: hidden;
    border: 1px solid yellow;
}
#main_content {
    width: 250px;
    border: 1px solid #F00;
}
#side_content {   
    position: fixed;
    top: 0;
    right: 0;
    width: 200px;
    left: 50%;
    margin-left: 50px;
    height: 100%;
    border: 1px solid #0F0;
    border-collapse: collapse;
}