JSFiddle - React, Tailwind, and code Playground

HTML

<body>
<div id="header">
    <div id="title">Your Feedback</div>
    <div id="accountinfo"><a href="#">Registrati</a> o <a href="#">accedi</a></div>
</div>
<div id="blank"></div>
<div id="main" style="margin-right: auto; ">
    <h1>TITLE</h1>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
<h2>SOME TEXT</h2>
</div>
        
<div id="footer">
    BLABLA
</div>

CSS

body{
    background-color:#8cbfcf;
    margin: 0px 0px 0px 0px;
    overflow:hidden;
    }
#header{
    height: 60px;
    background-color:#70b0c3;
    position:fixed;
    box-shadow:#19343d 0px 1px 2px;
    width:100%;
    margin-left:0px;
    z-index:999;
    }
#accountinfo{
    position: absolute;
    right:10px;
    top: 0px;
    font-family: Happy Monkey, sans-serif;
    color:#EFF;
    text-shadow:#000 1px 1px 1px;
    font-size:18px;
    line-height: 60px;
    }
#blank{
     height:60px;
     width:100%;
    }
#main{
    height: 1500px;
    width:580px;
    margin-left:auto;
    margin-top:20px;
    background-color:#70b0c3;
    box-shadow: #254C58 1px 0px;
    border: #3C7D91 1px double;
    border-bottom:0px;
    opacity:0.9;
    padding:10px 10px 10px 10px;
    overflow-y: scroll;
    max-height: 400px;
    }
#leftside{
    top: 80px;
    left: 160px;
    float: left;
    height: auto;
    width: 230px;
    background-color: #70B0C3;
    opacity: 0.9;
    border: #3C7D91 1px double;
    position:fixed;
    box-shadow: #254C58 1px 1px;
    border-radius: 5px 5px 5px 5px;
    }
#rightside{
    position:fixed;
    top:80px;
    right:160px;
    height:300px;
    width:230px;
    opacity: 0.9;
    background-color: #70B0C3;
    border: #3C7D91 1px double;
    box-shadow: #254C58 1px 1px;
    border-radius: 5px 5px 5px 5px;
    }