JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Positioning</title>
    <link rel="stylesheet" href="positioning.css">
</head>
<body>
    <nav></nav>
    <div id="container">
        <div id="topbar"></div>
        <div id="blocks">
            <div></div>
            <div></div>
            <div></div>
            <div></div>
            <div></div>
            <div></div>
        </div>
    </div>
    <footer></footer>
</body>
</html>

CSS

body {
    margin: 0px 0px;
}
nav {
    height: 100px;
    background-color: blue;
    width: 100%;
}

#container {
    border: 2px solid black;
    width: 90%;
    margin: 40px auto;
}

#topbar {
    width: 100%;
    height: 200px;
    background-color: lightgray;
}

#blocks div {
    width: 200px;
    background-color: lightgray;
    height: 200px;
    display: inline-block;
    margin-top: 5px;
}

footer {
    height: 100px;
    background-color: blue;
    width: 100%;
}