JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html  lang="en">
<head>
    <meta charset="UTF-8">
    <title>Centering-example</title>
    <link rel="stylesheet" type="text/css" href="centering-example.css" id="cssfile">
</head>
<body>
<div id="big_wrapper">
    <header id="top_header">
        <p id="centering_example">centering help</p>
        <a id="SELECTED" class="button" href="index.html">Home</a>
        <a class="button">Games</a>
        <a class="button">About us</a>
        <a class="button">Blog</a>

    </header>

    <div id="new_div">

        <section id="main_section">
            <article>
                <p>This is text for the index page of the website.</p>
                <br>
            </article>

        </section>

    </div>

    <footer id="the_footer">
        <h6>Footer text</h6>
        <a class="media_button" href="https://www.twitter.com">Twitter</a>
        <a class="media_button" href="https://www.facebook.com">Facebook</a>
        <a class="media_button" href="http://steamcommunity.com">Steam Group</a>
    </footer>
</div>

</body>
</html>

CSS

*{
    margin: 0;
    padding: 0;
}
h1{
    font: bold 20px Tahoma
}
h2{
    font: bold 20px Tahoma
}
header, section, footer, aside, nav, article {
    display: block;
}
html{
    height: 100%;
    background: rgb(143, 143, 143);
}
body{
    width: 100%;
    display: flex;
    justify-content: center;
}
#big_wrapper{
    margin: 0 0;
    display: flex;
    flex-direction: column;
    flex: 100%;

}
#top_header{
    position: fixed;
    text-align: center;
    top: 0;
    left: 0;
    right: 0;
    width: 400px;
    height: 120px;
    margin: 0 auto;
    background: rgb(45,45,45);
    /*border-bottom: 15px solid rgba(79, 79, 79, 0.4);*/
    border-radius: 8px;
    padding: 10px;
    /*box-shadow: rgb(30, 30, 30) 10px 10px 10px;*/
    font-family: Impact, sans-serif;
    font-size: 40px;
    color: white;
}
#centering_example{
    color: #a00d01;
    font-size: 45px;
    text-shadow: rgba(0,0,0,.5) -3px 3px 0;
}
#new_div{
    display: flex;
    flex-direction: row;
}
#main_section{
    position: relative;
    z-index: -1;
    top: 140px;
    max-width: 1200px;
    border-top-left-radius: 10px;
    border-top-right-radius: 10px;
    flex: 1;
    margin: auto;
    margin-top: 20px;
    padding: 20px;
    background: #3c3c3c;
    box-shadow: rgb(30, 30, 30) 10px 10px 10px;
}
#the_footer{
    position: relative;
    top: 140px;
    max-width: 1200px;
    margin: auto;
    text-align: center;
    padding: 20px;
    border-bottom-left-radius: 10px;
    border-bottom-right-radius: 10px;
    border-top: 1px solid black;
    background: #3c3c3c;
    box-shadow: rgb(30, 30, 30) 10px 10px 10px;
}
#SELECTED{
    display: inline-block;
    margin: 6px;
    margin-left: 5px;
    margin-right: 5px;
    border: 1px solid black;
    border-top: 1px solid #000000;
    border-top-color: rgba(0, 0, 0, 0.7);
    background: rgba(36,34,31, 0.6);
    box-shadow: rgba(0,0,0,1) 0 0 0;;
    padding: 9px 18px;
    border-radius: 8px;
    color: #f8f8f8;
    font-size: 16px;
   ...